Do not force using the C compiler as the linker

[ryandesign]

Forcing the C compiler as the linker fails when linking sq_static because the C++ standard library does not get linked in. By not forcing this, CMake gets to choose which compiler to use as the linker based on the languages of the files that comprise what is being linked, and in this case it will choose to use the C++ compiler, fixing the problem.

Fixes #290