gh-148557: Use em-config to locate trampoline clang (#148556)

When CC is wrapped by ccache, the Emscripten trampoline rule cannot derive the
matching clang path by treating CC as a single executable path. Query the active
LLVM toolchain path with em-config instead.

Author: clementperon

Makefile.pre.in

@@ -3139,7 +3139,7 @@ Python/asm_trampoline_universal2.o: $(srcdir)/Python/asm_trampoline_aarch64.S $(
 
 Python/emscripten_trampoline_inner.wasm: $(srcdir)/Python/emscripten_trampoline_inner.c
 	# emcc has a path that ends with emsdk/upstream/emscripten/emcc, we're looking for emsdk/upstream/bin/clang.
-	$$(dirname $$(dirname $(CC)))/bin/clang -o $@ $< -mgc -O2 -Wl,--no-entry -Wl,--import-table -Wl,--import-memory -target wasm32-unknown-unknown -nostdlib
+	$$(em-config LLVM_ROOT)/clang -o $@ $< -mgc -O2 -Wl,--no-entry -Wl,--import-table -Wl,--import-memory -target wasm32-unknown-unknown -nostdlib
 
 Python/emscripten_trampoline_wasm.c: Python/emscripten_trampoline_inner.wasm
 	$(PYTHON_FOR_REGEN) $(srcdir)/Platforms/emscripten/prepare_external_wasm.py $< $@ getWasmTrampolineModule