mk: Pass CFLAGS for target, not host

This changes the CFLAGS and related variables passed to compiletest to be passed
for the target, not the host, so we can correctly test 32-bit cross compiles on
64-bit host machines.

Hopefuly fixes #33379

Author: alexcrichton

mk/tests.mk

@@ -636,11 +636,11 @@ CTEST_COMMON_ARGS$(1)-T-$(2)-H-$(3) := \
         --host-rustcflags "$(RUSTC_FLAGS_$(3)) $$(CTEST_RUSTC_FLAGS) -L $$(RT_OUTPUT_DIR_$(3))" \
         --lldb-python-dir=$(CFG_LLDB_PYTHON_DIR) \
         --target-rustcflags "$(RUSTC_FLAGS_$(2)) $$(CTEST_RUSTC_FLAGS) -L $$(RT_OUTPUT_DIR_$(2))" \
-	--cc '$$(CC_$(3))' \
-	--cxx '$$(CXX_$(3))' \
-	--cflags "$$(CFG_GCCISH_CFLAGS_$(3))" \
-	--llvm-components "$$(LLVM_ALL_COMPONENTS_$(3))" \
-	--llvm-cxxflags "$$(LLVM_CXXFLAGS_$(3))" \
+	--cc '$$(CC_$(2))' \
+	--cxx '$$(CXX_$(2))' \
+	--cflags "$$(CFG_GCCISH_CFLAGS_$(2))" \
+	--llvm-components "$$(LLVM_ALL_COMPONENTS_$(2))" \
+	--llvm-cxxflags "$$(LLVM_CXXFLAGS_$(2))" \
         $$(CTEST_TESTARGS)
 
 ifdef CFG_VALGRIND_RPASS