[mips] Fix sem_init_glibc test for MIPS.

[sdardis]

Summary

glibc changed the implementation of semaphores for glibc 2.21 requiring
some target specific changes for this compiler-rt test. Modify the test
to cope with MIPS64 and do some future/correctness work by tying the
define for MIPS64 to exactly the define of __HAVE_64B_ATOMICS in glibc.

Contributions from Nitesh Jain.

[sdardis]

The line (defined(__mips64) || _MIPS_SIM == _ABI64) is due to the change[1] where Joseph Myers defined N32 (an IPL32 ABI for MIPS64) to not have 64 bit atomics to deal with the issues of alignment of semaphores.

[1] https://sourceware.org/git/?p=glibc.git;a=commit;h=df34134284b46cdd8ffd39551b858652d465ca08

[nitesh.jain]

Thanks Simon.

test/sanitizer_common/TestCases/Linux/sem_init_glibc.cc

 // RUN: %clangxx -O0 -g %s -lutil -o %t && %run %t
 // This test depends on the glibc layout of struct sem_t and checks that we
 // don't leave sem_t::private uninitialized.
 // UNSUPPORTED: android, lsan-x86
 #include <features.h>
 #include <assert.h>
 #include <semaphore.h>
 #include <string.h>
 #include <stdint.h>
 
 // On powerpc64be semval_t must be 64 bits even with "old" versions of glibc.
 #if __PPC64__ && __BIG_ENDIAN__
 typedef uint64_t semval_t;
 
 // This condition needs to correspond to __HAVE_64B_ATOMICS macro in glibc.
-#elif (defined(__x86_64__) || defined(__aarch64__) || defined(__powerpc64__) || \
-     defined(__s390x__) || defined(__sparc64__) || defined(__alpha__) || \
-     defined(__ia64__) || defined(__m68k__)) && __GLIBC_PREREQ(2, 21)
+#elif (defined(__x86_64__) || defined(__aarch64__) ||                          \
+       defined(__powerpc64__) || defined(__s390x__) || defined(__sparc64__) || \
+       defined(__alpha__) || defined(__ia64__) || defined(__m68k__) ||         \
+       (defined(__mips64) || _MIPS_SIM == _ABI64)) &&                          \
+    __GLIBC_PREREQ(2, 21)
 typedef uint64_t semval_t;
 #else
 typedef unsigned semval_t;
 #endif
 
 // glibc 2.21 has introduced some changes in the way the semaphore value is
 // handled for 32-bit platforms, but since these changes are not ABI-breaking
 // they are not versioned. On newer platforms such as ARM, there is only one