Introduce a cache of the configuration

You may have noticed that running make is a little slow. Every time
that it is loaded, it will try to detect everything again. So,
instead, save the output and reload it the next time.

This is implemented by adding a rule that (re-)creates the
config.cache file, which is included by make. If the file doesn't
exist yet, make will first run the rule which creates it, then reload
itself.

You can also cause it to reconfigure by running "make configure".

Signed-off-by: Thiago Macieira <thiago@macieira.org>

.gitignore

@@ -22,3 +22,4 @@ Documentation/user-manual.pdf
 Documentation/user-manual.text
 packaging/windows/subsurface.nsi
 packaging/macos/Info.plist
+config.cache

Configure.mk

@@ -1,5 +1,6 @@
 # -*- Makefile -*-
 # This file contains the detection rules
+all:
 
 PKGCONFIG=pkg-config
 XML2CONFIG=xml2-config
@@ -8,6 +9,11 @@ QMAKE=qmake
 MOC=moc
 UIC=uic
 
+CONFIGFILE = config.cache
+ifeq ($(CONFIGURING),1)
+
+# Detect the target system
+# Ask the compiler what OS it's producing files for
 UNAME := $(shell $(CC) -dumpmachine 2>&1 | grep -E -o "linux|darwin|win|gnu|kfreebsd")
 
 # find libdivecomputer
@@ -110,3 +116,45 @@ ZIPFLAGS = $(strip $(shell $(PKGCONFIG) --cflags libzip 2> /dev/null))
 
 LIBSQLITE3 = $(shell $(PKGCONFIG) --libs sqlite3 2> /dev/null)
 SQLITE3FLAGS = $(strip $(shell $(PKGCONFIG) --cflags sqlite3))
+
+# Write the configure file
+all: configure
+configure $(CONFIGURE): Configure.mk
+	@echo "\
+	CONFIGURED = 1 \\\
+	UNAME = $(UNAME) \\\
+	LIBDIVECOMPUTERDIR = $(LIBDIVECOMPUTERDIR) \\\
+	LIBDIVECOMPUTERCFLAGS = $(LIBDIVECOMPUTERCFLAGS) \\\
+	LIBDIVECOMPUTER = $(LIBDIVECOMPUTER) \\\
+	LIBQT = $(LIBQT) \\\
+	QTCXXFLAGS = $(QTCXXFLAGS) \\\
+	LIBGTK = $(LIBGTK) \\\
+	GTKCFLAGS = $(GTKCFLAGS) \\\
+	LIBGCONF2 = $(LIBGCONF2) \\\
+	GCONF2CFLAGS = $(GCONF2CFLAGS) \\\
+	GTK_MAC_BUNDLER = $(GTK_MAC_BUNDLER) \\\
+	LIBXML2 = $(LIBXML2) \\\
+	LIBXSLT = $(LIBXSLT) \\\
+	XML2CFLAGS = $(XML2CFLAGS) \\\
+	GLIB2CFLAGS = $(GLIB2CFLAGS) \\\
+	XSLCFLAGS = $(XSLCFLAGS) \\\
+	OSMGPSMAPFLAGS = $(OSMGPSMAPFLAGS) \\\
+	LIBOSMGPSMAP = $(LIBOSMGPSMAP) \\\
+	LIBSOUPCFLAGS = $(LIBSOUPCFLAGS) \\\
+	LIBSOUP = $(LIBSOUP) \\\
+	LIBZIP = $(LIBZIP) \\\
+	ZIPFLAGS = $(ZIPFLAGS) \\\
+	LIBSQLITE3 = $(LIBSQLITE3) \\\
+	SQLITE3FLAGS = $(SQLITE3FLAGS) \\\
+	" | sed 's,\\,\n,g' > $(CONFIGFILE)
+
+else
+configure $(CONFIGFILE): Configure.mk
+	@test -e $(CONFIGFILE) && echo Reconfiguring.. || echo Configuring...
+	@$(MAKE) CONFIGURING=1 configure
+	@echo Done
+
+-include $(CONFIGFILE)
+endif
+
+.PHONY: configure all

Rules.mk

@@ -197,4 +197,7 @@ clean:
 		$(VERSION_FILE) qt-ui/*.moc qt-ui/ui_*.h
 	rm -rf share .dep
 
+confclean: clean
+	rm -f $(CONFIGFILE)
+
 -include $(DEPS)