Allow glibc to be built with _FORTIFY_SOURCE

Add --enable-fortify-source option.

It is now possible to enable fortification through a configure option.
The level may be given as parameter, if none is provided, the configure
script will determine what is the highest level possible that can be set
considering GCC built-ins availability and set it.
If level is explicitly set to 3, configure checks if the compiler
supports the built-in function necessary for it or raise an error if it
isn't.

If the configure option isn't explicitly enabled, it _FORTIFY_SOURCE is
forcibly undefined (and therefore disabled).

The result of the configure checks are new variables, ${fortify_source}
and ${no_fortify_source} that can be used to appropriately populate
CFLAGS.

A dedicated patch will follow to make use of this variable in Makefiles
when necessary.

Updated NEWS and INSTALL.

Adding dedicated x86_64 variant that enables the configuration.

Reviewed-by: Siddhesh Poyarekar <siddhesh@sourceware.org>

1 files changed, 6 insertions, 0 deletions

diff --git a/NEWS b/NEWS
index 709ee40e50..f976abccbd 100644
--- a/NEWS
+++ b/NEWS
@@ -48,6 +48,12 @@ Major new features:
 * The strlcpy and strlcat functions have been added.  They are derived
   from OpenBSD, and are expected to be added to a future POSIX version.
 
+* A new configure option, "--enable-fortify-source", can be used to build the
+  GNU C Library with _FORTIFY_SOURCE. The level of fortification can either be
+  provided, or is set to the highest value supported by the compiler. If not
+  explicitly enabled, then fortify source is forcibly disabled so to keep
+  original behavior unchanged.
+
 Deprecated and removed features, and other changes affecting compatibility:
 
 * In the Linux kernel for the hppa/parisc architecture some of the