[LDC] BOLT runtime: Build libbolt_rt_instr_osx.a on Mac only

As compilation fails otherwise for Azure CI Linux and Android:

/usr/include/features.h:424:12: fatal error: 'sys/cdefs.h' file not found

Author: kinke

bolt/runtime/CMakeLists.txt

@@ -30,7 +30,7 @@ target_include_directories(bolt_rt_hugify PRIVATE ${CMAKE_CURRENT_BINARY_DIR})
 install(TARGETS bolt_rt_instr DESTINATION lib)
 install(TARGETS bolt_rt_hugify DESTINATION lib)
 
-if (CMAKE_CXX_COMPILER_ID MATCHES ".*Clang.*")
+if (APPLE)
   add_library(bolt_rt_instr_osx STATIC
     instr.cpp
     ${CMAKE_CURRENT_BINARY_DIR}/config.h