bpo-44131: Fix Makefile for test_frozenmain (GH-26203)

Remove Programs/test_frozenmain.h Makefile target: it ran make
in parallel which caused build errors on LTO+PGO builds.

Author: vstinner

Makefile.pre.in

@@ -720,15 +720,13 @@ Makefile Modules/config.c: Makefile.pre \
 	@mv config.c Modules
 	@echo "The Makefile was updated, you may need to re-run make."
 
+.PHONY: regen-test-frozenmain
 regen-test-frozenmain: $(BUILDPYTHON)
 	# Regenerate Programs/test_frozenmain.h
 	# from Programs/test_frozenmain.py
 	# using Programs/freeze_test_frozenmain.py
 	$(RUNSHARED) ./$(BUILDPYTHON) Programs/freeze_test_frozenmain.py Programs/test_frozenmain.h
 
-Programs/test_frozenmain.h: Programs/freeze_test_frozenmain.py Programs/test_frozenmain.py
-	$(MAKE) regen-test-frozenmain
-
 Programs/_testembed: Programs/_testembed.o $(LIBRARY_DEPS)
 	$(LINKCC) $(PY_CORE_LDFLAGS) $(LINKFORSHARED) -o $@ Programs/_testembed.o $(BLDLIBRARY) $(LIBS) $(MODLIBS) $(SYSLIBS)
 

Programs/test_frozenmain.h

@@ -1,3 +1,6 @@
+# Script used to test Py_FrozenMain(): see test_embed.test_frozenmain().
+# Run "make regen-test-frozenmain" if you modify this test.
+
 import sys
 import _testinternalcapi