build_environment: ffi/linux force predictable lib path.

ffi stubbornly wants to put libs in lib64 even when you tell it not to on some linux distributions.
patch based on sed fix the gentoo guys did [1]

[1] https://bugs.gentoo.org/462814

build_files/build_environment/cmake/ffi.cmake

@@ -25,8 +25,10 @@ ExternalProject_Add(external_ffi
 		--enable-shared=no
 		--enable-static=yes
 		--with-pic
+		--libdir=${LIBDIR}/ffi/lib/
 	BUILD_COMMAND ${CONFIGURE_ENV} && cd ${BUILD_DIR}/ffi/src/external_ffi/ && make -j${MAKE_THREADS}
 	INSTALL_COMMAND ${CONFIGURE_ENV} && cd ${BUILD_DIR}/ffi/src/external_ffi/ && make install
+	PATCH_COMMAND ${PATCH_CMD} -p 0 -d ${BUILD_DIR}/ffi/src/external_ffi < ${PATCH_DIR}/ffi.diff
 	INSTALL_DIR ${LIBDIR}/ffi
 )
 

build_files/build_environment/patches/ffi.diff

@@ -0,0 +1,11 @@
+--- Makefile.in	2014-11-12 06:59:58.000000000 -0500
++++ Makefile.in	2018-09-17 13:36:10.974086554 -0400
+@@ -600,7 +600,7 @@
+ target_os = @target_os@
+ target_vendor = @target_vendor@
+ toolexecdir = @toolexecdir@
+-toolexeclibdir = @toolexeclibdir@
++toolexeclibdir = $(libdir)
+ top_build_prefix = @top_build_prefix@
+ top_builddir = @top_builddir@
+ top_srcdir = @top_srcdir@