x86: Add support to build strcmp/strlen/strchr with explicit ISA level

1. Add default ISA level selection in non-multiarch/rtld
   implementations.

2. Add ISA level build guards to different implementations.
    - I.e strcmp-avx2.S which is ISA level 3 will only build if
      compiled ISA level <= 3. Otherwise there is no reason to
      include it as we will always use one of the ISA level 4
      implementations (strcmp-evex.S).

3. Refactor the ifunc selector and ifunc implementation list to use
   the ISA level aware wrapper macros that allow functions below the
   compiled ISA level (with a guranteed replacement) to be skipped.

Tested with and without multiarch on x86_64 for ISA levels:
{generic, x86-64-v2, x86-64-v3, x86-64-v4}

And m32 with and without multiarch.

1 files changed, 29 insertions, 0 deletions

diff --git a/sysdeps/x86_64/wcsncmp-generic.c b/sysdeps/x86_64/wcsncmp-generic.c
new file mode 100644
index 0000000000..493a6f9b9b
--- /dev/null
+++ b/sysdeps/x86_64/wcsncmp-generic.c
@@ -0,0 +1,29 @@
+/* wcsncmp dispatch for RTLD and non-multiarch .c ISA level 1 build.
+   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/>.  */
+
+/* wcsncmp non-multiarch build is split into two files,
+   wcsncmp-generic.c and wcsncmp.S. The wcsncmp-generic.c build is for
+   ISA level <= 1 and just uses wcsmbs/wcsncmp.c.  This must be split
+   into two files because we cannot include C code from assembly or
+   vice versa.  */
+
+#include <isa-level.h>
+
+#if MINIMUM_X86_ISA_LEVEL <= 2
+# include "wcsmbs/wcsncmp.c"
+#endif