build: fix includedir in pkgconfig file

We want to include via <apk/$headerfile> and not via <$headerfile>,
so we want to add an include statement for the dir the apk folder
which contains the headers is contained in.

Makefile

@@ -17,7 +17,7 @@ LIBDIR		:= /lib
 CONFDIR		:= /etc/apk
 MANDIR		:= /usr/share/man
 DOCDIR		:= /usr/share/doc/apk
-INCLUDEDIR	:= /usr/include/apk
+INCLUDEDIR	:= /usr/include
 PKGCONFIGDIR	:= /usr/lib/pkgconfig
 
 export DESTDIR SBINDIR LIBDIR CONFDIR MANDIR DOCDIR INCLUDEDIR PKGCONFIGDIR

src/Makefile

@@ -114,8 +114,8 @@ install: $(obj)/apk $(libapk_so) $(libapk_a) $(apklua_so)
 	$(install-libapk_so)
 	$(install-libapk_a)
 	$(install-apklua_so)
-	$(INSTALLDIR) $(DESTDIR)$(INCLUDEDIR)
-	$(INSTALL) -m644 src/*.h $(DESTDIR)$(INCLUDEDIR)
+	$(INSTALLDIR) $(DESTDIR)$(INCLUDEDIR)/apk
+	$(INSTALL) -m644 src/*.h $(DESTDIR)$(INCLUDEDIR)/apk
 	$(INSTALLDIR) $(DESTDIR)$(PKGCONFIGDIR)
 	$(INSTALL) -m644 $(obj)/apk.pc $(DESTDIR)$(PKGCONFIGDIR)
 

src/apk.pc.in

@@ -7,4 +7,4 @@ Description: Alpine Package Manager
 Version: @VERSION@
 Requires: zlib openssl
 Libs: -L${libdir} -lapk
-Cflags: -I${includedir}/apk
+Cflags: -I${includedir}