Log Message:
math/ltm: Fix build caused by improper use of $(PREFIX).

The makefile.include fragment included by all of the project
makefiles unconditionally sets $(CC), $(LD), $(AR) and $(RANLIB)
to $(PREFIX){gcc,ld,ar,ranlib}.  Their intent was to provide a
facility for cross-compiling the code, but the use of $(PREFIX)
for this purpose was unfortunate.

This change adds a patch to set $(PREFIX) to the empty string in
the makefiles, which should fix the problem with the smallest
set of changes.