fix "gcc: error: : No such file or directory"

Because I wasn't specifying --cppopts, 'cppopts opts' was "", so the
first value given to language-c's runPreprocessor was [""]. This caused
language-c to run gcc with ["-o","/tmp/xxx.i","-E","xxx.h",""] (note the
final ""), which caused gcc to die with "error: : No such file or
directory".
Merge pull request #4 from bsl/master

Fix bad behavior when --cppopts unspecified