[CMake] When disabling PIC, also pass -fno-pie when linking if it is supported.

Building clang with -fno-pie generates slightly faster code. In my not-very-rigorous testing I saw about a 4% speed up using the clang test-suite sources.

llvm-svn: 253959

llvm/cmake/config-ix.cmake

@@ -299,6 +299,10 @@ if( LLVM_ENABLE_PIC )
   set(ENABLE_PIC 1)
 else()
   set(ENABLE_PIC 0)
+  check_cxx_compiler_flag("-fno-pie" SUPPORTS_NO_PIE_FLAG)
+  if(SUPPORTS_NO_PIE_FLAG)
+    list(APPEND CMAKE_EXE_LINKER_FLAGS "-fno-pie")
+  endif()
 endif()
 
 check_cxx_compiler_flag("-Wno-variadic-macros" SUPPORTS_NO_VARIADIC_MACROS_FLAG)