The check-syntax target is enabled the use of Flymake's "legacy"
backend, flymake-proc-legacy-flymake in src/*.c. It works quite well
with C sources. The green light for this change had already been
given some time ago in
https://lists.gnu.org/archive/html/emacs-devel/2017-10/msg00385.html
* src/Makefile.in (check-syntax): New target.
(.PHONY): Add check-syntax.
endif
@: Compile some files earlier to speed up further compilation.
$(MAKE) -C ../lisp compile-first EMACS="$(bootstrap_exe)"
+
+### Flymake support (for C only)
+check-syntax:
+ $(AM_V_CC)$(CC) -c $(CPPFLAGS) $(ALL_CFLAGS) ${CHK_SOURCES} || true
+.PHONY: check-syntax