gst-glib-gen.mak: fix build with GNU make 4.3
GNU make 4.3 introduced an incompatibility with how # works inside a function invocation: http://git.savannah.gnu.org/cgit/make.git/tree/NEWS?h=4.3#n19
This causes spurious backslashes in the generated *-enumtypes.c, causing build failures.
To fix this on GNU make 4.3 while retaining compatibility for 4.2, use a separate variable to store the # symbol. This is workaround suggested in the incompatibility note.
Fixes #6 (closed).
Edited by Michael Forney