[distcc] -x argument processing bug

[Ben Scarlet]

In args.c, distcc uses !strcmp(a, "-x") to check for gcc's language
specification flag. However, gcc accepts languages both with and without
whitespace separating the -x from the language. For example, a Makefile
might say
g++ -x c++ -c foo.c -o foo.o
to get foo.c compiled as c++, but it could also say
g++ -xc++ -c foo.c -o foo.o

It would be nice to implement the fancy -x rewriting proposed in the top of
the file, but in the meantime I suggest the strict equality comparison be
replaced with str_startswith("-x", a)

	Ben Scarlet