add a macro that really identifies glibc

base/process_util_linux.cc

Index: base/process_util_linux.cc
diff --git a/base/process_util_linux.cc b/base/process_util_linux.cc
index 2c2824fd77db68da521883918bc88b580e99caa2..2bed9453befe7e5775dae8df685bf9450a0bc4bb 100644
--- a/base/process_util_linux.cc
+++ b/base/process_util_linux.cc
@@ -745,7 +745,7 @@ void OnNoMemory() {
 
 }  // namespace
 
-#if !defined(OS_ANDROID) && !defined(USE_TCMALLOC) && \
+#if defined(GLIBC) && !defined(USE_TCMALLOC) && \

[agl, 2013/05/20 15:18:22]

It's not clear that we don't actually want this malloc behaviour on Android. It
may have been an expedient choice during porting that hasn't been fixed.

It's doubly not clear that we don't want this malloc behaviour for uClibc in
general. We might need to do a dlsym dance to get the original pointers, but
that's very different than just disabling it. 

[Mostyn Bramley-Moore, 2013/05/20 20:41:41]

I downloaded android-ndk-r8e and inspected
platforms/android-14/arch-arm/usr/lib/libc.so - it does not have any of the
__libc_* symbols used below.  Similarly for the x86 version, and also with
uClibc.  So it seems safe to say that this code will only work with glibc,
though I don't have definitive documentation of this.  
You're probably right, but I think this might be better implemented in a
followup task.  Would you settle for a TODO note inside some rearranged ifdefs?
ie something like:

#if !defined(ADDRESS_SANITIZER) && !defined(MEMORY_SANITIZER) &&
!defined(THREAD_SANITIZER)

#if defined(GLIBC) && !defined(USE_TCMALLOC)
... make use of __libc_* ...
#else
// TODO: dylsym dance
#endif

#endif

     !defined(ADDRESS_SANITIZER) && !defined(MEMORY_SANITIZER) && \
     !defined(THREAD_SANITIZER)
 
@@ -826,7 +826,7 @@ int posix_memalign(void** ptr, size_t alignment, size_t size) {
 }
 
 }  // extern C
-#endif  // ANDROID, TCMALLOC, *_SANITIZER
+#endif  // GLIBC, !TCMALLOC, !*_SANITIZER
 
 void EnableTerminationOnHeapCorruption() {
   // On Linux, there nothing to do AFAIK.