[libFuzzer CMake] NFC Declare LIBFUZZER_FLAGS_BASE outside of an if-block

[george.karpenkov]

Summary

The current code relies on the assumption that tests are included only if LLVM_USE_SANITIZE_COVERAGE is enabled.
This commit makes it easier to relax the assumption in the future, as the variable LIBFUZZER_FLAGS_BASE is used further in libFuzzer tests CMakeLists.txt.

[kcc]

LGTM

lib/Fuzzer/CMakeLists.txt

 include(CheckCXXSourceCompiles)
 
 if( APPLE )
   CHECK_CXX_SOURCE_COMPILES("
       static thread_local int blah;
       int main() {
         return 0;
       }
       " HAS_THREAD_LOCAL)
 
   if( NOT HAS_THREAD_LOCAL )
     set(CMAKE_CXX_FLAGS "${CMAKE_CXX_FLAGS} -Dthread_local=__thread")
   endif()
 endif()
 
+set(LIBFUZZER_FLAGS_BASE "${CMAKE_CXX_FLAGS}")
 if( LLVM_USE_SANITIZE_COVERAGE )
   if(NOT "${LLVM_USE_SANITIZER}" STREQUAL "Address")
     message(FATAL_ERROR
       "LibFuzzer and its tests require LLVM_USE_SANITIZER=Address and "
       "LLVM_USE_SANITIZE_COVERAGE=YES to be set."
       )
   endif()
-  set(LIBFUZZER_FLAGS_BASE "${CMAKE_CXX_FLAGS}")
 
   # Disable the coverage and sanitizer instrumentation for the fuzzer itself.
   set(CMAKE_CXX_FLAGS "${LIBFUZZER_FLAGS_BASE} -fno-sanitize-coverage=trace-pc-guard,edge,trace-cmp,indirect-calls,8bit-counters -Werror")
 endif()
 
 # Compile libFuzzer if the compilation is specifically requested, OR
 # if the platform is known to be working.
 if ( LLVM_USE_SANITIZE_COVERAGE OR CMAKE_SYSTEM_NAME MATCHES "Darwin|Linux" )