Merge pull request #1989 from hauke/libffi

libffi: fix libffi.pc file

libs/libffi/patches/001-fix-includedir-pkg.patch

@@ -0,0 +1,11 @@
+--- a/libffi.pc.in
++++ b/libffi.pc.in
+@@ -1,7 +1,7 @@
+ prefix=@prefix@
+ exec_prefix=@exec_prefix@
+ libdir=@libdir@
+-includedir=${libdir}/@PACKAGE_NAME@-@PACKAGE_VERSION@/include
++includedir=${prefix}/include
+ 
+ Name: @PACKAGE_NAME@
+ Description: Library supporting Foreign Function Interfaces