isl: move -lm at the end of tests_ldadd
isl: move -lm at the end of tests_ldadd

The test was failing to build with "undefined reference to `roundf'" errors,
so Make check on mesa was failing.

Reviewed-by: Jason Ekstrand <68c46a606457643eab92053c1c05574abb26f861@jlekstrand.net>

metora/MesaGLSLCompiler,metora/MesaGLSLCompiler,metora/MesaGLSLCompiler