[compiler-rt] Go back to using the 32-bit allocator for Fuchsia+RISCV64

[leonardchan]

Summary

Due to logic in the 64-bit allocator, the smallest allocation we can zx_vmar_allocate is 2^37 bytes, but this is too large to allocate for the standalone lsan allocator on a 39-bit VMA. This leads to the zx_vmar_allocate call when initially setting up the allocator to fail. This is similar to what android experiences on a 64-bit system with a small vma. (See sanitizer_allocator_test.cpp).

This effectively reverts f6c4808d95221a5838e14474d95c6fe85bb1488a and has Fuchsia use the 32-bit allocator for RISCV.

[leonardchan]

Woops. Forgot to add the differential revision: bit to the commit, but this was submitted in 17623e96b5b84c0868fe6b4a1456e3d7da275c95.

compiler-rt/lib/sanitizer_common/sanitizer_platform.h

 #endif
 
 // By default we allow to use SizeClassAllocator64 on 64-bit platform.
 // But in some cases SizeClassAllocator64 does not work well and we need to
 // fallback to SizeClassAllocator32.
 // For such platforms build this code with -DSANITIZER_CAN_USE_ALLOCATOR64=0 or
 // change the definition of SANITIZER_CAN_USE_ALLOCATOR64 here.
 #ifndef SANITIZER_CAN_USE_ALLOCATOR64
-#  if (SANITIZER_RISCV64 && !SANITIZER_FUCHSIA) || SANITIZER_IOS
+#  if SANITIZER_RISCV64 || SANITIZER_IOS
 #    define SANITIZER_CAN_USE_ALLOCATOR64 0
 #  elif defined(__mips64) || defined(__hexagon__)
 #    define SANITIZER_CAN_USE_ALLOCATOR64 0
 #  else
 #    define SANITIZER_CAN_USE_ALLOCATOR64 (SANITIZER_WORDSIZE == 64)
 #  endif
 #endif