configure does not honor CC when testing for -mcmodel=large

[Seth Goldberg]

Hi,

 Setting $CC to another gcc (not in the path) fails when attempting to 
configure for 64-bit EFI if the installed gcc cannot handle -mcmodel=large. 
configure.in should be changed to honor $CC.  I'm horrible at m4 / autoconf, 
so I'm not sure what needs to be changed (otherwise, I'd provide a patch :)).

 From config.log after running ( setenv CC gcc-4.3.2; ./configure 
--with-platform=efi --target=x86_64):

configure:6612: result: no
configure:6617: WARNING: -mcmodel=large not supported. You won't be able to use 
the memory over 4GiB. Upgrade your gcc
configure:6624: checking whether option -mno-red-zone works
configure:6652: gcc -c -Os -m64 -DMCMODEL_SMALL=1 -m64 -mno-red-zone  conftest.c 
>&5
conftest.c:1: sorry, unimplemented: 64-bit mode not compiled in


 --S