libbz2: add pkg-config file (bzip2.pc)

Add generation of a bzip2.pc file for use with pkg-config and create
a basic template as bzip2.pc.in.

This allows other software to easily locate and link against libbz2
using standard pkg-config mechanisms instead of manual compiler and
linker flags.

The version number is extracted automatically from bzlib.h to keep
it consistent with the library sources.

Tested:	pkg-config --exists --print-errors "bzip2 >= 1.0.9" (fail, expected)
	pkg-config --exists --print-errors "bzip2 >= 1.0" (succeeded)
	pkg-config --libs bzip2 (-lbz2)
	pkg-config --cflags bzip2 ()

MFC after:	3 days

lib/libbz2/Makefile

@@ -13,4 +13,17 @@ CFLAGS+=	-I${BZ2DIR}
 
 WARNS?=		3
 
+BZIP2_VERSION!=	sed -n '/bzip2\/libbzip2 version /{s/.*version //;s/ of.*//p;q;}' ${BZ2DIR}/bzlib.h
+
+bzip2.pc: bzip2.pc.in
+	sed -e 's,@prefix@,/usr,g ; \
+		s,@exec_prefix@,$${prefix},g ; \
+		s,@libdir@,${LIBDIR},g ; \
+		s,@sharedlibdir@,${SHLIBDIR},g ; \
+		s,@includedir@,${INCLUDEDIR},g ; \
+		s,@VERSION@,${BZIP2_VERSION},g ;' \
+		${.ALLSRC} > ${.TARGET}
+
+PCFILES=	bzip2.pc
+
 .include <bsd.lib.mk>

lib/libbz2/bzip2.pc.in

@@ -0,0 +1,11 @@
+prefix=@prefix@
+exec_prefix=@exec_prefix@
+libdir=@libdir@
+sharedlibdir=@sharedlibdir@
+includedir=@includedir@
+
+Name: bzip2
+Description: bzip2 compression library
+Version: @VERSION@
+Libs: -L${libdir} -lbz2
+Cflags: -I${includedir}