[Tests] Attempt to fix PowerPC buildbots.

The intent is that the tests should not be running on PowerPC as the fp128 type
will differ. This attempts to fix the bots by using __powerpc__ instead, which
appears to be defined in godbolt.

Author: davemgreen

llvm/cmake/config-ix.cmake

@@ -260,7 +260,7 @@ if(C_SUPPORTS_WERROR_UNGUARDED_AVAILABILITY_NEW)
 endif()
 
 check_cxx_symbol_exists(logf128 cmath HAS_LOGF128)
-check_symbol_exists(__powerpc64le__ "" __PPC64LE)
+check_symbol_exists(__powerpc__ "" __PPC64LE)
 if(HAS_LOGF128 AND NOT __PPC64LE)
     set(LLVM_HAS_LOGF128 On)
     add_compile_definitions(HAS_LOGF128)