ffmpeg: Fix pkgconfig files to be more cross compile friendly

Before:

prefix=/usr
exec_prefix=${prefix}
libdir=/usr/lib
includedir=/usr/include

After:

prefix=/usr
exec_prefix=/usr
libdir=${exec_prefix}/lib
includedir=${prefix}/include

Numbered the other patch file.

Signed-off-by: Rosen Penev <rosenp@gmail.com>

multimedia/ffmpeg/Makefile

@@ -10,7 +10,7 @@ include $(TOPDIR)/rules.mk
 
 PKG_NAME:=ffmpeg
 PKG_VERSION:=3.4.6
-PKG_RELEASE:=3
+PKG_RELEASE:=4
 
 PKG_SOURCE:=$(PKG_NAME)-$(PKG_VERSION).tar.xz
 PKG_SOURCE_URL:=https://ffmpeg.org/releases/

multimedia/ffmpeg/patches/010-pkgconfig.patch

@@ -0,0 +1,15 @@
+--- a/ffbuild/pkgconfig_generate.sh
++++ b/ffbuild/pkgconfig_generate.sh
+@@ -28,9 +28,9 @@ version=$(grep ${name}_VERSION= $name/${name}.version | cut -d= -f2)
+ 
+ cat <<EOF > $name/$fullname.pc
+ prefix=$prefix
+-exec_prefix=\${prefix}
+-libdir=$libdir
+-includedir=$incdir
++exec_prefix=${prefix}
++libdir=\${exec_prefix}/lib
++includedir=\${prefix}/include
+ 
+ Name: $fullname
+ Description: $comment