[ubsan] Enable UBSan build for Fuchsia

[mcgrathr]

This is rebased and ready to land.
Please land it for me!

Thanks,
Roland

[vitalybuka]

Could you please remove unnecessary "dependent revision" here and in other CLs.
I guess this is the reason why "arc patch" does not work

[vitalybuka]

arc patch D36033

I have:
Checking patch compiler-rt/trunk/lib/sanitizer_common/sanitizer_platform_interceptors.h...
error: compiler-rt/trunk/lib/sanitizer_common/sanitizer_platform_interceptors.h: does not exist in index
Checking patch compiler-rt/trunk/lib/sanitizer_common/sanitizer_common_interceptors.inc...
error: compiler-rt/trunk/lib/sanitizer_common/sanitizer_common_interceptors.inc: does not exist in index

Patch Failed!
Usage Exception: Unable to apply patch!

compiler-rt/trunk/cmake/config-ix.cmake

 if (COMPILER_RT_HAS_SANITIZER_COMMON AND TSAN_SUPPORTED_ARCH AND
     OS_NAME MATCHES "Darwin|Linux|FreeBSD|Android")
   set(COMPILER_RT_HAS_TSAN TRUE)
 else()
   set(COMPILER_RT_HAS_TSAN FALSE)
 endif()
 
 if (COMPILER_RT_HAS_SANITIZER_COMMON AND UBSAN_SUPPORTED_ARCH AND
-    OS_NAME MATCHES "Darwin|Linux|FreeBSD|Windows|Android")
+    OS_NAME MATCHES "Darwin|Linux|FreeBSD|Windows|Android|Fuchsia")
   set(COMPILER_RT_HAS_UBSAN TRUE)
 else()
   set(COMPILER_RT_HAS_UBSAN FALSE)
 endif()
 
 if (COMPILER_RT_HAS_SANITIZER_COMMON AND SAFESTACK_SUPPORTED_ARCH AND
     OS_NAME MATCHES "Darwin|Linux|FreeBSD")
   set(COMPILER_RT_HAS_SAFESTACK TRUE)

compiler-rt/trunk/lib/ubsan/ubsan_platform.h

 #define UBSAN_PLATFORM_H
 
 // Other platforms should be easy to add, and probably work as-is.
 #if (defined(__linux__) || defined(__FreeBSD__) || defined(__APPLE__)) && \
     (defined(__x86_64__) || defined(__i386__) || defined(__arm__) || \
      defined(__aarch64__) || defined(__mips__) || defined(__powerpc64__) || \
      defined(__s390__))
 # define CAN_SANITIZE_UB 1
-#elif defined(_WIN32)
+#elif defined(_WIN32) || defined(__Fuchsia__)
 # define CAN_SANITIZE_UB 1
 #else
 # define CAN_SANITIZE_UB 0
 #endif
 
 #endif