gst-glib-gen.mak broken with GNU make 4.3

The offending line is

enum_headers=$(foreach h,$(glib_enum_headers),\n\#include \"$(h)\")

On GNU make 4.2, the escaped \# is necessary to avoid a syntax error. On GNU make 4.3, the backslash is not necessary, and it's presence causes stray backslashes in the generated *-enumtypes.c, resulting in syntax errors when compiling.

The incompatibility is documented (along with a suggested workaround) at http://git.savannah.gnu.org/cgit/make.git/tree/NEWS?h=4.3#n18.