[NFC] Makefile.defs: Improve omptest search path building

Use `clang -print-resource-dir` instead of manual path building
 - supported since at least version 18 of clang

Author: mhalk

test/Makefile.defs

@@ -387,8 +387,8 @@ else
 endif
 
 # ompTest: Set header include path + linker flag for corresponding OMPT tests
-CLANG_VERSION := $(lastword $(sort $(notdir $(patsubst %/,%,$(dir $(wildcard $(AOMP)/lib/clang/*/))))))
-OMPTEST = -I$(AOMP)/lib/clang/$(CLANG_VERSION)/include/omptest -lomptest
+CLANG_RESOURCE_DIR ?= $(shell $(AOMP)/bin/clang -print-resource-dir)
+OMPTEST            ?= -I$(CLANG_RESOURCE_DIR)/include/omptest -lomptest
 
 # ompTest: Set and export CMake config path
 omptest_DIR = $(AOMP)/lib/cmake/openmp/omptest/