After updating to ML and Xcode 4.5.1, can't compile anything

Question

Hi, hoping someone here will be able to give me a clue.
I used to compile a unix program called ffmpeg and about 12 dependencies.  It is somewhat complex, but I have a script for updating the programs.  When Lion came out I had to make some minor changes, including specifying --cc=clang in the ffmpeg configure step.  Now with Mountain Lion and Xcode 4.5.1 I can't compile anything.
Rather than downloading and installing the command-line tools, which I understand just duplicate what is in Xcode, I added /Applications/Xcode.app/Contents/Developer/usr/bin to my path so that any configuration script would be able to get to the tools.
Nothing is compiling at all.  Basically the compiler fails some tests in the scripts.  Each program gives different error messages, but it all looks like the compiler is wrong.
Strangely, when I investigated the compilers in the above directory, I found that gcc (I guess the default) is an alias to llvm-gcc-4.2, in another folder.  But when I just type gcc in a terminal, I get:
i686-apple-darwin11-llvm-gcc-4.2: no input files
So it is actually using a different compiler for reasons I don't understand, and I don't know if that is correct behavior, or if it is related to my inability to compile.
In case it is not obvious, I am just knowledgeable enough to be dangerous with this stuff.
Thanks,
Jim

Answer 1

Gee, you mean you can't believe everything you read on the internet?? ;-)
Well you're right.  After installing the tools, all the programs appeared to compile fine . . . except ffmpeg.  The terminal response at the end is
gcc is unable to create an executable file.
If gcc is a cross-compiler, use the --enable-cross-compile option.
Only do this if you know what cross compiling means.
C compiler test failed.
The config.log starts with the configure command:
./configure --prefix=/Volumes/Ramdisk/sw --enable-nonfree --enable-gpl --enable-version3 --arch=x86_64 --enable-hardcoded-tables --enable-libvo-aacenc --enable-libmp3lame --enable-libx264 --enable-libvorbis --enable-libgsm --enable-avfilter --enable-filters --enable-libtheora --enable-libspeex --disable-indevs --disable-outdevs --disable-ffserver --disable-network
And ends with:
check_ld cc
check_cc
BEGIN /var/folders/sy/2d072p1s4sdc95lpnwp6s3jh0000gn/T//ffconf.huTMXBG3.c
    1          int main(void){ return 0; }
END /var/folders/sy/2d072p1s4sdc95lpnwp6s3jh0000gn/T//ffconf.huTMXBG3.c
gcc -I/Volumes/Ramdisk/sw/include
-c -o /var/folders/sy/2d072p1s4sdc95lpnwp6s3jh0000gn/T//ffconf.ZC6xNAgf.o /var/folders/sy/2d072p1s4sdc95lpnwp6s3jh0000gn/T//ffconf.huTMXBG3.c
i686-apple-darwin11-llvm-gcc-4.2: \n: No such file or directory
C compiler test failed.
Any idea what's wrong now?  The compiler still seems to be wrong for this program.  This is the program for which in the past, I had to add --cc=clang - but now if I do that it just says "clang is unable . . ." instead of "gcc is unable . . ."
The next to last line in the config.log has me puzzled though - a newline tripping it up?