c_build_helper: Split cc command line

Optionally the CC/HOSTCC environment variable can hold the command to
invoke the C compiler, however this command can also contain extra
arguments, not only the binary name. In this particular case Python
was treating the whole value as a single binary name, and was trying
to execute as such (e.g. "cc -arg1 -arg2" instead of "cc" and the arguments
separately), which results in failure.

Split the compiler command into its components to invoke it correctly.

Signed-off-by: Gyorgy Sarvari <skandigraun@gmail.com>