Add .clang-format style file

Went with version >= 11.0 since it covers most of the major features
and should be pretty universally accessibly.

There are some issues:

1.  indention of preprocessor directives:
    Unfortunately there doesn't appear to be a switch for a seperate
    'IndentWidth' for preprocessor directives vs. normal code so we
    are stuck either not indenting the directives or over-indenting
    them. i.e:
    Desired:
    ```
    #ifndef A
    # define B
    #endif
    ```
    Options:
    ```
    #ifndef A
    #  define B /* Two spaces instead of one.  */
    #endif

    #ifndef C
    #define D   /* No spaces.  */
    #endif
    ```
    Chose to over-indent as it generally seems easier to script
    halving all pre-processor indentations than counting the nested
    depth and indenting from scratch.

2.  concatenation of lines missing semi-colons:
    Throughout glibc there are macros used to setup aliasing that are
    outside of functions and don't end in semi-colons i.e:
    ```
    libc_hidden_def (__pthread_self)
    weak_alias (__pthread_self, pthread_self)
    ```

    clang-format reformats lines like these to:
    ```
    libc_hidden_def (__pthread_self) weak_alias (__pthread_self, pthread_self)
    ```

    which is generally undesirable.

Other than those two big concerns there are certainly some questions
diffs but for the most part it creates a easy to read and consistent
style.
Reviewed-by: Carlos O'Donell <carlos@redhat.com>

1 files changed, 156 insertions, 0 deletions

diff --git a/.clang-format b/.clang-format
new file mode 100644
index 0000000000..79530b305a
--- /dev/null
+++ b/.clang-format
@@ -0,0 +1,156 @@
+#  clang-format file for GLIBC
+#  Copyright (C) 2022 Free Software Foundation, Inc.
+#  This file is part of the GNU C Library.
+#
+#  The GNU C Library is free software; you can redistribute it and/or
+#  modify it under the terms of the GNU Lesser General Public
+#  License as published by the Free Software Foundation; either
+#  version 2.1 of the License, or (at your option) any later version.
+#
+#  The GNU C Library is distributed in the hope that it will be useful,
+#  but WITHOUT ANY WARRANTY; without even the implied warranty of
+#  MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
+#  Lesser General Public License for more details.
+#
+#  You should have received a copy of the GNU Lesser General Public
+#  License along with the GNU C Library; if not, see
+#  <https://www.gnu.org/licenses/>.
+#
+#  Requires clang-format version >= 11.0
+#
+#  For more information, see:
+#
+#   https://clang.llvm.org/docs/ClangFormat.html
+#   https://clang.llvm.org/docs/ClangFormatStyleOptions.html
+#
+#  There are some known cases that this doesn't produce the desired
+#  style (i.e Preprocessor Directives are over-indented and not
+#  auto-commented). As a result, this is meant to be a utility to make
+#  formatting easier, not a definitive standard.
+#
+#  To format the current git diff inplace (-i) the follow command can
+#  be used:
+#  $> git diff -U0 --no-color HEAD^ | clang-format-diff -i -p1
+#
+#  To just view the diff clang-format would generate:
+#  $> git diff -U0 --no-color HEAD^ | clang-format-diff -p1
+#
+#  NB: clang-format-diff, along with other clang-format related tools,
+#      can be found at: /path/to/llvm-project/clang/tools/clang-format/
+#
+#
+#  Based on autogenerated format from:
+#  $> clang-format --style=GNU -dump-config
+---
+AccessModifierOffset: -2
+AlignAfterOpenBracket: Align
+AlignConsecutiveMacros: false
+AlignConsecutiveAssignments: false
+AlignConsecutiveBitFields: false
+AlignConsecutiveDeclarations: false
+AlignEscapedNewlines: Right
+AlignOperands:   true
+AlignTrailingComments: true
+AllowAllArgumentsOnNextLine: true
+AllowAllParametersOfDeclarationOnNextLine: true
+AllowShortEnumsOnASingleLine: true
+AllowShortBlocksOnASingleLine: false
+AllowShortCaseLabelsOnASingleLine: false
+AllowShortFunctionsOnASingleLine: All
+AllowShortLambdasOnASingleLine: All
+AllowShortIfStatementsOnASingleLine: Never
+AllowShortLoopsOnASingleLine: false
+AlwaysBreakAfterDefinitionReturnType: All
+AlwaysBreakAfterReturnType: AllDefinitions
+AlwaysBreakBeforeMultilineStrings: false
+BinPackArguments: true
+BinPackParameters: true
+BraceWrapping:
+  AfterCaseLabel:  true
+  AfterClass:      true
+  AfterControlStatement: true
+  AfterEnum:       true
+  AfterFunction:   true
+  AfterNamespace:  true
+  AfterStruct:     true
+  AfterUnion:      true
+  AfterExternBlock: true
+  BeforeCatch:     true
+  BeforeElse:      true
+  BeforeWhile:     true
+  IndentBraces:    true
+  SplitEmptyFunction: true
+  SplitEmptyRecord: true
+  SplitEmptyNamespace: true
+BreakBeforeBinaryOperators: All
+BreakBeforeBraces: GNU
+BreakBeforeInheritanceComma: false
+BreakInheritanceList: BeforeColon
+BreakBeforeTernaryOperators: true
+BreakStringLiterals: true
+ColumnLimit:     79
+CommentPragmas:  '^ IWYU pragma:'
+CompactNamespaces: false
+ContinuationIndentWidth: 4
+Cpp11BracedListStyle: false
+DeriveLineEnding: true
+DerivePointerAlignment: false
+DisableFormat:   false
+ExperimentalAutoDetectBinPacking: false
+FixNamespaceComments: false
+IncludeBlocks:   Preserve
+IncludeCategories:
+  - Regex:           '.*'
+    Priority:        1
+IncludeIsMainRegex: '(Test)?$'
+IndentCaseLabels: false
+IndentCaseBlocks: false
+IndentGotoLabels: true
+IndentWidth:     2
+IndentPPDirectives: AfterHash
+IndentExternBlock: AfterExternBlock
+IndentWrappedFunctionNames: false
+InsertTrailingCommas: None
+KeepEmptyLinesAtTheStartOfBlocks: true
+MacroBlockBegin: ''
+MacroBlockEnd:   ''
+MaxEmptyLinesToKeep: 1
+NamespaceIndentation: None
+PenaltyBreakAssignment: 2
+PenaltyBreakBeforeFirstCallParameter: 19
+PenaltyBreakComment: 300
+PenaltyBreakFirstLessLess: 120
+PenaltyBreakString: 1000
+PenaltyExcessCharacter: 1000000
+PenaltyReturnTypeOnItsOwnLine: 60
+PointerAlignment: Right
+ReflowComments:  true
+SortIncludes:    false
+SortUsingDeclarations: true
+SpaceAfterCStyleCast: true
+SpaceAfterLogicalNot: false
+SpaceBeforeAssignmentOperators: true
+SpaceBeforeCpp11BracedList: false
+SpaceBeforeCtorInitializerColon: true
+SpaceBeforeInheritanceColon: true
+SpaceBeforeParens: Always
+SpaceBeforeRangeBasedForLoopColon: true
+SpaceInEmptyBlock: false
+SpaceInEmptyParentheses: false
+SpacesBeforeTrailingComments: 1
+SpacesInAngles:  false
+SpacesInConditionalStatement: false
+SpacesInContainerLiterals: true
+SpacesInCStyleCastParentheses: false
+SpacesInParentheses: false
+SpacesInSquareBrackets: false
+SpaceBeforeSquareBrackets: false
+Standard:        Cpp03
+TabWidth:        8
+UseTab:          Always
+ForEachMacros:
+  - 'FOR_EACH_IMPL'
+  - 'list_for_each'
+  - 'list_for_each_prev'
+  - 'list_for_each_prev_safe'
+...