Retrieve location of gen_gccbuiltins from CMake.

This is required for the MSVC build because binaries are placed in a Debug or Release folder.

CMakeLists.txt

@@ -303,6 +303,7 @@ target_link_libraries(gen_gccbuiltins "-lLLVMTableGen -lLLVMSupport -ldl ${LLVM_
 
 # For use by the druntime/Phobos build system.
 get_target_property(LDC_LOC ${LDC_EXE} LOCATION)
+get_target_property(GEN_GCCBUILTINS_LOC gen_gccbuiltins LOCATION)
 
 #
 # LDMD

runtime/CMakeLists.txt

@@ -268,8 +268,8 @@ macro(build_runtime d_flags c_flags ld_flags lib_suffix path_suffix)
         set(GCCBUILTINS "${PROJECT_BINARY_DIR}/gccbuiltins_x86.di")
         add_custom_command(
             OUTPUT ${GCCBUILTINS}
-            COMMAND ${PROJECT_BINARY_DIR}/../bin/gen_gccbuiltins ${GCCBUILTINS} "x86"
-            DEPENDS ${PROJECT_BINARY_DIR}/../bin/gen_gccbuiltins
+            COMMAND ${GEN_GCCBUILTINS_LOC} ${GCCBUILTINS} "x86"
+            DEPENDS ${GEN_GCCBUILTINS_LOC}
         )
         if(BUILD_SINGLE_LIB)
             add_library(${RUNTIME_AIO}${target_suffix}