tools lib subcmd: Add dependency test to install_headers

Compute the headers to be installed from their source headers and make
each have its own build target to install it. Using dependencies
avoids headers being reinstalled and getting a new timestamp which
then causes files that depend on the header to be rebuilt.
Signed-off-by: Ian Rogers <irogers@google.com>
Cc: Alexander Shishkin <alexander.shishkin@linux.intel.com>
Cc: Ingo Molnar <mingo@redhat.com>
Cc: Jiri Olsa <jolsa@kernel.org>
Cc: Josh Poimboeuf <jpoimboe@kernel.org>
Cc: Mark Rutland <mark.rutland@arm.com>
Cc: Masahiro Yamada <masahiroy@kernel.org>
Cc: Namhyung Kim <namhyung@kernel.org>
Cc: Nathan Chancellor <nathan@kernel.org>
Cc: Nick Desaulniers <ndesaulniers@google.com>
Cc: Nicolas Schier <nicolas@fjasle.eu>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Stephane Eranian <eranian@google.com>
Cc: Tom Rix <trix@redhat.com>
Cc: bpf@vger.kernel.org
Cc: llvm@lists.linux.dev
Link: https://lore.kernel.org/r/20221202045743.2639466-4-irogers@google.comSigned-off-by: Arnaldo Carvalho de Melo <acme@redhat.com>

tools/lib/subcmd/Makefile

@@ -89,10 +89,10 @@ define do_install_mkdir
 endef
 
 define do_install
-	if [ ! -d '$(DESTDIR_SQ)$2' ]; then             \
-		$(INSTALL) -d -m 755 '$(DESTDIR_SQ)$2'; \
+	if [ ! -d '$2' ]; then             \
+		$(INSTALL) -d -m 755 '$2'; \
 	fi;                                             \
-	$(INSTALL) $1 $(if $3,-m $3,) '$(DESTDIR_SQ)$2'
+	$(INSTALL) $1 $(if $3,-m $3,) '$2'
 endef
 
 install_lib: $(LIBFILE)
@@ -100,13 +100,16 @@ install_lib: $(LIBFILE)
 		$(call do_install_mkdir,$(libdir_SQ)); \
 		cp -fpR $(LIBFILE) $(DESTDIR)$(libdir_SQ)
 
-install_headers:
-	$(call QUIET_INSTALL, libsubcmd_headers) \
-		$(call do_install,exec-cmd.h,$(prefix)/include/subcmd,644); \
-		$(call do_install,help.h,$(prefix)/include/subcmd,644); \
-		$(call do_install,pager.h,$(prefix)/include/subcmd,644); \
-		$(call do_install,parse-options.h,$(prefix)/include/subcmd,644); \
-		$(call do_install,run-command.h,$(prefix)/include/subcmd,644);
+HDRS := exec-cmd.h help.h pager.h parse-options.h run-command.h
+INSTALL_HDRS_PFX := $(DESTDIR)$(prefix)/include/subcmd
+INSTALL_HDRS := $(addprefix $(INSTALL_HDRS_PFX)/, $(HDRS))
+
+$(INSTALL_HDRS): $(INSTALL_HDRS_PFX)/%.h: %.h
+	$(call QUIET_INSTALL, $@) \
+		$(call do_install,$<,$(INSTALL_HDRS_PFX)/,644)
+
+install_headers: $(INSTALL_HDRS)
+	$(call QUIET_INSTALL, libsubcmd_headers)
 
 install: install_lib install_headers