Hi,

when testing I noticed, that if compile with both -fsanitize=address and 
-fstack-protector for 32-bit architectures and run with 
ASAN_OPTIONS=detect_stack_use_after_return=1, libsanitizer fails with:

  ==7299==AddressSanitizer CHECK failed: 
/home/max/workspace/downloads/gcc/libsanitizer/asan/asan_poisoning.cc:25 
"((AddrIsAlignedByGranularity(addr + size))) != (0)" (0x0, 0x0)
     #0 0xf72d8afc in AsanCheckFailed 
/home/max/workspace/downloads/gcc/libsanitizer/asan/asan_rtl.cc:68
     #1 0xf72dda89 in __sanitizer::CheckFailed(char const*, int, char 
const*, unsigned long long, unsigned long long) 
/home/max/workspace/downloads/gcc/libsanitizer/sanitizer_common/sanitizer_common.cc:72

This happens because ssp inserts a stack guard into a function, that 
confuses asan_emit_stack_protection to calculate right size parameter 
for asan_stack_malloc.

This tiny patch resolves the issue.

Regtested with make -j12 -k check 
RUNTESTFLAGS='--target_board=unix\{-m32,-m64\}' on x86_64-unknown-linux-gnu.

Bootstrapped, ASan-bootstrapped on x86_64-unknown-linux-gnu.

Ok to commit?

-Maxim