Add parts for GAP package build systems

The file Makefile.gappkg is already use by several GAP packages. By
shipping it with GAP, it gets easier for new GAP packages to provide
simple kernel extensions.

etc/Makefile.gappkg

@@ -0,0 +1,146 @@
+########################################################################
+#
+# The build rules in this file are intended for use by GAP packages that
+# want to build a simple GAP kernel extensions. They are based on the
+# GAP build system, and require GNU make. To use this in your GAP
+# package, `include` this from your primary Makefile. You must also set
+# several variables beforehand:
+#
+# - GAPPATH must be set to the location of the GAP installation against
+#   which to build your package.
+# - KEXT_NAME should be the name of your kernel extension (without
+#   file extensions like .so or .dll)
+# - KEXT_SOURCES must contain a list of .c or .cc files to be linked
+#   into your kernel extension
+# - optionally, you can set KEXT_CFLAGS, KEXT_CXXFLAGS, KEXT_LDFLAGS
+#
+#
+# Only GAP >= 4.11 ships with this file. In order to keep your package
+# compatible with older GAP versions, we recommend to bundle a copy of
+# it with your package, but only as a fallback. So, your configure
+# scripts should check if GAP ships with this file, and use it then, and
+# only fall back to your own copy as a last resort. This way, you will
+# benefit from any fixes and improvements made by the GAP team.
+#
+# The contents of this file are released into the public domain; hence
+# you may edit this file as you wish, bundle and distribute it with your
+# package, etc.
+#
+# If you bundle this file with your package, please try not to edit it,
+# so that we can keep it identical across all GAP packages. If you still
+# find that you must edit it, please consider submitting your changes
+# back to the GAP team, so that a future version of this file can be
+# adjusted to cover your usecase without modifications.
+#
+########################################################################
+
+# read GAP's build settings
+include $(GAPPATH)/sysinfo.gap
+
+# various derived settings
+KEXT_BINARCHDIR = bin/$(GAParch)
+KEXT_SO = $(KEXT_BINARCHDIR)/$(KEXT_NAME).so
+
+GAP = $(GAPPATH)/gap
+GAC = $(GAPPATH)/gac
+
+# override KEXT_RECONF if your package needs a different invocation
+# for reconfiguring (e.g. `./config.status --recheck` for autoconf)
+KEXT_RECONF ?= ./configure "$(GAPPATH)"
+
+# default target
+all: $(KEXT_SO)
+.PHONY: all
+
+########################################################################
+# Object files
+# For each file FOO.c in SOURCES, add gen/FOO.lo to KEXT_OBJS; similar
+# for .cc files
+########################################################################
+KEXT_OBJS = $(patsubst %.cc,gen/%.lo,$(patsubst %.c,gen/%.lo,$(KEXT_SOURCES)))
+
+########################################################################
+# Quiet rules.
+#
+# Replace regular output with quiet messages, unless V is set,
+# e.g. "make V=1"
+########################################################################
+ifneq ($(findstring $(MAKEFLAGS),s),s)
+ifndef V
+QUIET_GAC     = @echo "   GAC     $< => $@";
+endif
+endif
+
+########################################################################
+# Rules for automatic header dependency tracking.
+# This is based on the GAP build system.
+########################################################################
+
+# List of all (potential) dependency directories, derived from KEXT_OBJS
+# and KEXT_SOURCES (the latter for generated sources, which may also
+# involve dependency tracking)
+KEXT_DEPDIRS = $(sort $(dir $(KEXT_SOURCES) $(KEXT_OBJS)))
+KEXT_DEPFILES = $(wildcard $(addsuffix /*.d,$(KEXT_DEPDIRS)))
+
+# Include the dependency tracking files.
+-include $(KEXT_DEPFILES)
+
+# Mark *.d files as PHONY. This stops make from trying to recreate them
+# (which it can't), and in particular from looking for potential source
+# files. This can save quite a bit of disk access time.
+.PHONY: $(KEXT_DEPFILES)
+
+# The following flags instruct the compiler to enable advanced
+# dependency tracking. Supported by GCC 3 and newer; clang; Intel C
+# compiler; and more.
+KEXT_DEPFLAGS = -MQ "$@" -MMD -MP -MF $(@D)/$(*F).d
+
+# build rule for C code
+# The dependency on Makefile ensures that re-running configure recompiles everything
+gen/%.lo: %.c Makefile
+	$(QUIET_GAC)$(GAC) -d -p "$(KEXT_DEPFLAGS)" -p "$(KEXT_CFLAGS)" -c $< -o $@
+
+# build rule for C++ code
+# The dependency on Makefile ensures that re-running configure recompiles everything
+gen/%.lo: %.cc Makefile
+	$(QUIET_GAC)$(GAC) -d -p "$(KEXT_DEPFLAGS)" -p "$(KEXT_CXXFLAGS)" -c $< -o $@
+
+# build rule for linking all object files together into a kernel extension
+$(KEXT_SO): $(KEXT_OBJS)
+	@mkdir -p $(KEXT_BINARCHDIR)
+	$(QUIET_GAC)$(GAC) -d -p "$(KEXT_DEPFLAGS)" -P "$(KEXT_LDFLAGS)" $(KEXT_OBJS) -o $@
+
+# hook into `make clean`
+clean: clean-kext
+clean-kext:
+	rm -rf $(KEXT_BINARCHDIR) gen
+
+# hook into `make distclean`
+distclean: clean-kext
+distclean-kext:
+	rm -rf bin gen Makefile
+	(cd doc && ./clean)
+
+# hook into `make doc`
+doc: doc-kext
+doc-kext:
+	$(GAP) makedoc.g
+
+# hook into `make check`
+check: check-kext
+check-kext:
+	$(GAP) tst/testall.g
+
+# re-run configure if configure, Makefile.in or GAP itself changed
+Makefile: configure Makefile.in $(GAPPATH)/sysinfo.gap
+	$(KEXT_RECONF)
+
+.PHONY: check clean distclean doc
+.PHONY: check-kext clean-kext distclean-kext doc-kext
+
+########################################################################
+# Makefile debugging trick:
+# call print-VARIABLE to see the runtime value of any variable
+########################################################################
+print-%:
+	@echo '$*=$($*)'