runtime(make): do not automatically indent after a special target

prevent indentation if the previous line starts with e.g. `.PHONY:`

closes: #17183

Signed-off-by: Eisuke Kawashima <e-kwsm@users.noreply.github.com>
Signed-off-by: Christian Brabandt <cb@256bit.org>

runtime/indent/testdir/make.in

@@ -0,0 +1,20 @@
+# vim:ft=make
+# START_INDENT
+.POSIX :
+MAKEFLAGS += -rR
+
+.SUFFIXES: .F .f
+FC = f95
+FFLAGS =
+CPPFLAGS =
+
+.PHONY: help
+help:
+@echo indentation test
+
+.F.f:
+$(FC) $(CPPFLAGS) -E $< > $@
+
+.f.o:
+$(FC) $(FFLAGS) -c -o $@ $<
+# END_INDENT

runtime/indent/testdir/make.ok

@@ -0,0 +1,20 @@
+# vim:ft=make
+# START_INDENT
+.POSIX :
+MAKEFLAGS += -rR
+
+.SUFFIXES: .F .f
+FC = f95
+FFLAGS =
+CPPFLAGS =
+
+.PHONY: help
+help:
+	@echo indentation test
+
+.F.f:
+	$(FC) $(CPPFLAGS) -E $< > $@
+
+.f.o:
+	$(FC) $(FFLAGS) -c -o $@ $<
+# END_INDENT