[wasm][stdlib] Add -D_WASI_EMULATED_PROCESS_CLOCKS to CFLAGS

Stubs.cpp includes <sys/resource.h> which requires the emulation in
wasi-libc

Author: kateinoigakukun

stdlib/cmake/modules/AddSwiftStdlib.cmake

@@ -323,7 +323,7 @@ function(_add_target_variant_c_compile_flags)
   endif()
 
   if("${CFLAGS_SDK}" STREQUAL "WASI")
-    list(APPEND result "-D_WASI_EMULATED_MMAN")
+    list(APPEND result "-D_WASI_EMULATED_MMAN" "-D_WASI_EMULATED_PROCESS_CLOCKS")
   endif()
 
   if(NOT SWIFT_STDLIB_ENABLE_OBJC_INTEROP)