build: support make help-overrides-option and help-overrides-header

Add a make help-overrides-option which reports certain configuration
variables (those relating to external libraries) in a different format, as
if they were configure options.

HAVE_FOO_BAR is printed as

--have-foo-bar	...

This is used by the configure script to provide two formats for such options
(expected to be more necessary when they are needed at all, due to the lack
of useful automatic replacements for such libraries), via ENV_OVERRIDES or
--configure-options=.

We split the header emitted at the top of make help-overrides off into make
help-overrides-header because the configure script will want to emit the
header before the help-overrides-option output (which is printed first).

Signed-off-by: Nick Alcock <nick.alcock@oracle.com>
Reviewed-by: Kris Van Hees <kris.van.hees@oracle.com>

Makeconfig

@@ -30,6 +30,23 @@ help-overrides::
 	       "$$$$(printf "%s" "$(2)" | sed 's,(.*),,g')" >&2
 endef
 
+# Emit a help rule for an override's config option.
+#
+# Syntax: $(call make-overrride-option-help,var,help-string)
+define make-override-option-help
+help-overrides-option::
+	width=$$$$(printf -- '--with-$(1)=[yes/no]' | wc -c); \
+	tabs=""; \
+	if [[ $$$${width} -gt 31 ]]; then \
+	    tabs=' '; \
+	elif [[ $$$${width} -gt 23 ]]; then \
+	    tabs='\t'; \
+	elif [[ $$$${width} -gt 15 ]]; then \
+	    tabs='\t\t'; \
+	fi; \
+	printf -- "--with-%s=[yes/no]$$$${tabs}Override check for$(2)\n" "$$$$(printf -- '$(1)' | LC_COLLATE=C tr '[A-Z_]' '[a-z-]')" >&2
+endef
+
 # Generate a makefile rule to check for the presence of FUNCTION
 # in HEADER and emit an appropriate header file fragment into a
 # file under $(objdir)/.config.
@@ -73,7 +90,14 @@ endef
 # The first argument must be suitable for a filename fragment,
 # for a makefile rule name and for a #define.
 #
-# Syntax: $(call check-symbol-rule,name,symbol,library)
+# Also emit a rule to print help for this override to standard
+# error, and (if OPTION) is set, a rule to print help for
+# this override in standard configure --with-* form.  (This is
+# used for options relating to things for which we do not have
+# compatibility fallbacks, for which configure-style --with-*
+# options seem particularly desirable.)
+#
+# Syntax: $(call check-symbol-rule,name,symbol,library,option)
 define check-symbol-rule
 $(objdir)/.config/config.$(1).h $(objdir)/.config/config.$(1).mk: $(objdir)/.config/.dir.stamp
 	val="$(HAVE_$(1))"; \
@@ -97,6 +121,8 @@ $(objdir)/.config/config.$(1).h $(objdir)/.config/config.$(1).mk: $(objdir)/.con
 	rm -f $(CONFIG_MK)
 
 $(eval $(call make-override-help,HAVE_$(1), presence of $(2) in lib$(3)))
+$(if $(4),
+  $(eval $(call make-override-option-help,$(1), presence of $(2) in $(3).h)),)
 
 $(CONFIG_H): $(objdir)/.config/config.$(1).h
 $(CONFIG_MK): $(objdir)/.config/config.$(1).mk
@@ -152,16 +178,16 @@ $(CONFIG_MK):
 	echo 'CONFIGURED := yes' >> $(objdir)/config.mk
 	cat $(objdir)/.config/*.mk >> $(objdir)/config.mk 2>/dev/null || true
 
-help-overrides::
+help-overrides-header::
 	printf "Overrides for library and symbol searches:\n\n" >&2
 
 $(eval $(call check-symbol-rule,ELF_GETSHDRSTRNDX,elf_getshdrstrndx,elf))
-$(eval $(call check-symbol-rule,LIBCTF,ctf_open,ctf))
+$(eval $(call check-symbol-rule,LIBCTF,ctf_open,ctf,t))
 $(eval $(call check-symbol-rule,STRRSTR,strrstr,c))
-$(eval $(call check-symbol-rule,LIBSYSTEMD,sd_notify,systemd))
+$(eval $(call check-symbol-rule,LIBSYSTEMD,sd_notify,systemd,t))
 ifndef WANTS_LIBFUSE2
 $(eval $(call check-symbol-rule,FUSE_LOG,fuse_set_log_func,fuse3))
-$(eval $(call check-symbol-rule,LIBFUSE3,fuse_session_receive_buf,fuse3))
+$(eval $(call check-symbol-rule,LIBFUSE3,fuse_session_receive_buf,fuse3,t))
 endif
 $(eval $(call check-header-rule,FUSE_NUMA,fuse_set_numa,fuse/fuse_lowlevel))
 $(eval $(call check-header-symbol-rule,CLOSE_RANGE,close_range(3,~0U,0),c,unistd))
@@ -174,4 +200,4 @@ $(eval $(call check-header-rule,INITDISINFO4,init_disassemble_info(NULL,NULL,NUL
 help-overrides::
 	printf "\n" >&2
 
-help:: help-overrides
+help:: help-overrides-header help-overrides