buildsys: add make install (WIP)

Makefile.rules

@@ -519,9 +519,10 @@ clean:
 
 LTINSTALL=$(LIBTOOL) --mode=install $(INSTALL)
 
-install:
-	@echo "Error, 'make install' has not yet been implemented"
-	exit 1
+install: install-bin install-gaproot install-headers install-libgap
+	@echo "+-----------------------------------------------------------------------+"
+	@echo "| WARNING, 'make install' support is incomplete! Use at your own peril! |"
+	@echo "+-----------------------------------------------------------------------+"
 
 # the following is wrapper script which is installed by the install-bin target
 define gap_wrapper
@@ -809,6 +810,23 @@ JULIA_LIBS="$(JULIA_LIBS)"
 endef
 export sysinfo_gap
 
+# FIXME: sysinfo.gap refactoring:
+# - split GAP_CPPFLAGS and move parts of them to GAP_INCLUDE_FLAGS,
+#   to make them easier to adjust for installation?
+# - get rid of GAP_OBJS by removing the "static link" feature from gac;
+#   i.e., retain comp_static but don't let it go till linking
+# - rename GAParch (but keep it for backwards compat)
+# - because of GAParch, we can't actually install sysinfo.gap into $prefix/lib
+#   it seems we may need at least two root dirs for installations, too;
+#   one which contains "sysinfo.gap" and other arch dependent files, and
+#   which is where one points configure scripts at; and one which contains
+#   the stuff which is portable; say
+#     GAP_BIN_DIR=$prefix/lib/gap/    contains sysinfo.gap, gap, gac
+#     GAP_LIB_DIR=$prefix/share/gap/  contains doc, grp, lib, ...
+#   Note how "lib" means two different things above...
+#
+#  So far, we can still "model" this quite well with sysinfo.gap; but I
+#  wonder if one day we might need to add provisions for more than two GAPROOTs ?
 all: sysinfo.gap
 sysinfo.gap: config.status $(srcdir)/Makefile.rules cnf/GAP-CFLAGS cnf/GAP-CPPFLAGS cnf/GAP-CXXFLAGS cnf/GAP-LDFLAGS cnf/GAP-LIBS
 	@rm -f sysinfo.gap	# in case this is a symlink created by an older version of the build system