[MPlayer-users] configure accepts bogus --cc values

[Roger Pack]

As a note, I accidentally ran into this today:
if you pass ./configure a --cc value that doesn't exist, it silently
falls back to the system cc:


 ./configure --cc=abc

make V=1
gcc -MMD -MP -Wundef -Wall -Wno-switch -Wno-parentheses
-Wpointer-arith -Wredundant-decls -Wstrict-prototypes

which was surprising and confused me for awhile until I noticed it.
Suggest failing if users pass in a bogus value there.
Other than that cross compiling worked, I'm able to generate 32 or 64
bit binaries via this script now:
https://github.com/rdp/ffmpeg-windows-build-helpers

Thank you.
-roger-