#102 Error starting semantic if gcc is not installed

[Lluís]

This is a hard one to catch, as I've only seen it while working on a fresh new machine where gcc was still not installed.

Debugger entered--Lisp error: (wrong-type-argument stringp nil)
file-name-directory(nil)
semantic-gcc-setup()
byte-code(...)
semantic-default-c-setup()
semantic-new-buffer-fcn()
run-hooks(mode-local-init-hook)
...

`file-name-directory' is failing due to `gcc-exe' being null (no gcc is installed on my system).

This should probably silently finish the procedure, with at most a message telling that gcc could not be found on the system.

[Eric M. Ludlam]

I made a small change that should fix this based on the stack trace, though I haven't reproduced this issue myself.