[CMake][fuzzer] Add riscv64 to fuzzer supported arch list

[kobrineli]

Summary

I tried to build libFuzzer for RISC-V and succeeded. All the libFuzzer
targets were successfully built. I tested this on the small hello world code
with a few branches to check the instrumentation; all of them were covered by
libFuzzer on RISC-V arch. So I suppose it makes sense to enable libFuzzer
build for RISC-V.

[phosek]

LGTM

[SweetVishnya]

Can we push this patch to main branch?

[kobrineli]

In D147788#4251769, @phosek wrote:

LGTM

@phosek @thetruestblue

Hi! Could you push this to the main branch, please? I don't have commit access

compiler-rt/cmake/Modules/AllSupportedArchDefs.cmake

 
 if(ANDROID)
   set(OS_NAME "Android")
 else()
   set(OS_NAME "${CMAKE_SYSTEM_NAME}")
 endif()
 
 if(OS_NAME MATCHES "Linux")
-  set(ALL_FUZZER_SUPPORTED_ARCH ${X86} ${X86_64} ${ARM32} ${ARM64} ${S390X})
+  set(ALL_FUZZER_SUPPORTED_ARCH ${X86} ${X86_64} ${ARM32} ${ARM64} ${S390X}
+      ${RISCV64})
 elseif (OS_NAME MATCHES "Windows")
   set(ALL_FUZZER_SUPPORTED_ARCH ${X86} ${X86_64})
 elseif(OS_NAME MATCHES "Android")
   set(ALL_FUZZER_SUPPORTED_ARCH ${X86} ${X86_64} ${ARM32} ${ARM64} ${RISCV64})
 else()
   set(ALL_FUZZER_SUPPORTED_ARCH ${X86_64} ${ARM64})
 endif()