build: add configure option pkgconfigdir

This allows the user to override the directory for the installation
of the pkg-config files (from the default LIBDIR/pkgconfig).

It follows the usual behaviour of Makefiles generated by automake.
Signed-off-by: Ingo Brückl <ib@wupperonline.de>
Reviewed-by: Andreas Cadhalpun <andreas.cadhalpun@googlemail.com>
Signed-off-by: Michael Niedermayer <michaelni@gmx.at>

configure

@@ -87,6 +87,7 @@ Standard options:
   --shlibdir=DIR           install shared libs in DIR [LIBDIR]
   --incdir=DIR             install includes in DIR [PREFIX/include]
   --mandir=DIR             install man page in DIR [PREFIX/share/man]
+  --pkgconfigdir=DIR       install pkg-config files in DIR [LIBDIR/pkgconfig]
   --enable-rpath           use rpath to allow installing libraries in paths
                            not part of the dynamic linker search path
                            use rpath when linking programs [USE WITH CARE]
@@ -1954,6 +1955,7 @@ PATHS_LIST="
     incdir
     libdir
     mandir
+    pkgconfigdir
     prefix
     shlibdir
 "
@@ -4487,6 +4489,7 @@ check_cpp_condition stdlib.h "defined(__PIC__) || defined(__pic__) || defined(PI
 
 set_default libdir
 : ${shlibdir_default:="$libdir"}
+: ${pkgconfigdir_default:="$libdir/pkgconfig"}
 
 set_default $PATHS_LIST
 set_default nm
@@ -5799,6 +5802,7 @@ BINDIR=\$(DESTDIR)$bindir
 DATADIR=\$(DESTDIR)$datadir
 DOCDIR=\$(DESTDIR)$docdir
 MANDIR=\$(DESTDIR)$mandir
+PKGCONFIGDIR=\$(DESTDIR)$pkgconfigdir
 SRC_PATH=$source_path
 ifndef MAIN_MAKEFILE
 SRC_PATH:=\$(SRC_PATH:.%=..%)

library.mak

@@ -90,8 +90,8 @@ install-lib$(NAME)-headers: $(addprefix $(SUBDIR),$(HEADERS) $(BUILT_HEADERS))
 	$$(INSTALL) -m 644 $$^ "$(INCINSTDIR)"
 
 install-lib$(NAME)-pkgconfig: $(SUBDIR)lib$(FULLNAME).pc
-	$(Q)mkdir -p "$(LIBDIR)/pkgconfig"
-	$$(INSTALL) -m 644 $$^ "$(LIBDIR)/pkgconfig"
+	$(Q)mkdir -p "$(PKGCONFIGDIR)"
+	$$(INSTALL) -m 644 $$^ "$(PKGCONFIGDIR)"
 
 uninstall-libs::
 	-$(RM) "$(SHLIBDIR)/$(SLIBNAME_WITH_MAJOR)" \
@@ -103,7 +103,7 @@ uninstall-libs::
 
 uninstall-headers::
 	$(RM) $(addprefix "$(INCINSTDIR)/",$(HEADERS) $(BUILT_HEADERS))
-	$(RM) "$(LIBDIR)/pkgconfig/lib$(FULLNAME).pc"
+	$(RM) "$(PKGCONFIGDIR)/lib$(FULLNAME).pc"
 	-rmdir "$(INCINSTDIR)"
 endef