Fix GPU build with MATRIX library

[ghbrown]

This PR adds necessary changes to fix failing GPU builds with the companion MATRIX library. The post fix version makes GNU builds on Illinois's campus cluster and my personal *nix machine. I suspect builds on other machines (Summit, etc.) are also going to be fixed by these changes, but I have yet to confirm on Summit.

Specifically, it adds the missing mmlatte_ Fortran interface for the CUDA matrix multiply routine, replacing the unused MATRIX/F_mmtest.cu. Without this addition one gets compile time errors like

/usr/bin/ld: pulay.o: in function `pulay_':
pulay.F90:(.text+0x1d52): undefined reference to `mmlatte_'
/usr/bin/ld: pulay.F90:(.text+0x1d81): undefined reference to `mmlatte_'
/usr/bin/ld: pulay.F90:(.text+0x1e11): undefined reference to `mmlatte_'
/usr/bin/ld: pulay.F90:(.text+0x1e3c): undefined reference to `mmlatte_'
/usr/bin/ld: pulay.F90:(.text+0x1e6b): undefined reference to `mmlatte_'
/usr/bin/ld: pulay.o:pulay.F90:(.text+0x1e92): more undefined references to `mmlatte_' follow
collect2: error: ld returned 1 exit status
make[1]: *** [Makefile:88: latte] Error 1

Further, it replaces the CUDA library path with a more generic version that probably better represents *nix systems (but will nevertheless have to be changed for most production machines), and links against the OpenMP library in the GPU options. Without the OpenMP link, one gets errors like

/usr/bin/ld: sparsemath.o: undefined reference to symbol 'GOMP_atomic_start@@GOMP_1.0'
/usr/bin/ld: /usr/lib/libgomp.so.1: error adding symbols: DSO missing from command line
collect2: error: ld returned 1 exit status
make[1]: *** [Makefile:88: latte] Error 1

[ghbrown]

After looking over outstanding issues, this PR addresses issue #107 .