package/gcc: fix build issue with glibc 2.26

package/gcc: fix build issue with glibc 2.26

../../../../libsanitizer/sanitizer_common/sanitizer_stoptheworld_linux_libcdep.cc: In function ‘int __sanitizer::TracerThread(void*)’:
../../../../libsanitizer/sanitizer_common/sanitizer_stoptheworld_linux_libcdep.cc:241:22: error: aggregate ‘sigaltstack handler_stack’ has incomplete type and cannot be defined
   struct sigaltstack handler_stack;

../../../../libsanitizer/sanitizer_common/sanitizer_stoptheworld_linux_libcdep.cc: In function ‘int __sanitizer::TracerThread(void*)’:
../../../../libsanitizer/sanitizer_common/sanitizer_stoptheworld_linux_libcdep.cc:276:22: error: aggregate ‘sigaltstack handler_stack’ has incomplete type and cannot be defined
   struct sigaltstack handler_stack;
                      ^~~~~~~~~~~~~

The fix is already included in gcc 7.2 release [1]. We have to backport it to
all older gcc release since it's not included in any stable release yet.

[1] https://gcc.gnu.org/git/?p=gcc.git;a=commit;h=72edc2c02f8b4768ad660f46a1c7e2400c0a8e06

Signed-off-by: Romain Naour <romain.naour@gmail.com>
Cc: Thomas Petazzoni <thomas.petazzoni@free-electrons.com>
Cc: "Yann E. MORIN" <yann.morin.1998@free.fr>
Reviewed-by: "Yann E. MORIN" <yann.morin.1998@free.fr>
Signed-off-by: Arnout Vandecappelle (Essensium/Mind) <arnout@mind.be>