simplify pkg-config library checking

rather than invoking pkg-config multiple times to check for libraries,
this invokes it just once.

the error message before this change (by changing imlib2 to imlib22 in
configure.ac):

	checking for imlib22... no
	configure: error: Package requirements (imlib22) were not met:

	pkg-config: could not find package 'imlib22'

the error message after this change (by changing imlib2 to imlib22 in
deps.pc):

	checking for ./deps.pc... no
	configure: error: Package requirements (./deps.pc) were not met:

	pkg-config: could not find package 'imlib22'

so there's no real loss of functionality here.

the reason for using `deps.pc` rather than just adding multiple
libraries in a single PKG_CHECK_MODULES is to reduce dependency on
autoconf.

additionally move the _XOPEN_SOURCE flag to deps.pc.

Author: N-R-K

Makefile.am

@@ -37,7 +37,7 @@ man_MANS = man/scrot.1
 
 dist_doc_DATA = AUTHORS ChangeLog CONTRIBUTING.md doc/scrot.png FAQ README.md TODO.md
 
-EXTRA_DIST = $(man_MANS) autogen.sh
+EXTRA_DIST = $(man_MANS) autogen.sh deps.pc
 
 SUBDIRS = src
 

configure.ac

@@ -27,15 +27,8 @@ AS_IF([test "x$orig_CFLAGS" = "x"], [
     AX_APPEND_LINK_FLAGS(["$SCROT_FLAGS"])
 ])
 
-AX_APPEND_COMPILE_FLAGS("-D_XOPEN_SOURCE=700L")
-
 # Checks for libraries.
-PKG_CHECK_MODULES([X11], [x11])
-PKG_CHECK_MODULES([XCOMPOSITE], [xcomposite])
-PKG_CHECK_MODULES([XEXT], [xext])
-PKG_CHECK_MODULES([XFIXES], [xfixes])
-PKG_CHECK_MODULES([XINERAMA], [xinerama])
-PKG_CHECK_MODULES([IMLIB2], [imlib2])
+PKG_CHECK_MODULES([SCROT_DEPS], ["$srcdir/deps.pc"])
 
 AC_ARG_ENABLE([libbsd-feature-test],
     AS_HELP_STRING([--enable-libbsd-feature-test],
@@ -60,10 +53,8 @@ AS_IF([test "x$LIBBSD_NEEDED" = "xyes"], [
         [AC_MSG_ERROR([BSD functions not found, libbsd is required])])
 ])
 
-AC_SUBST([LIBS], ["$X11_LIBS $XCOMPOSITE_LIBS $XEXT_LIBS $XFIXES_LIBS \
-    $XINERAMA_LIBS $IMLIB2_LIBS $LIBBSD_LIBS $LIBS"])
-AC_SUBST([CPPFLAGS], ["$X11_CFLAGS $XCOMPOSITE_CFLAGS $XEXT_CFLAGS \
-    $XFIXES_CFLAGS $XINERAMA_CFLAGS $IMLIB2_CFLAGS $LIBBSD_CFLAGS $CPPFLAGS"])
+AC_SUBST([LIBS], ["$SCROT_DEPS_LIBS $LIBBSD_LIBS $LIBS"])
+AC_SUBST([CPPFLAGS], ["$SCROT_DEPS_CFLAGS $LIBBSD_CFLAGS $CPPFLAGS"])
 
 AC_CONFIG_FILES([Makefile src/Makefile])
 AC_OUTPUT

deps.pc

@@ -0,0 +1,5 @@
+Name: scrot's mandatory dependencies
+Description: ditto
+Version: infinite
+Cflags: -D_XOPEN_SOURCE=700L
+Requires: x11 imlib2 xcomposite xext xfixes xinerama