Compiler vendor not detected properly when using conda tools

[marcinz]

When using conda tools, the following compiler version string is returned by GCC:

$ $CC --version
x86_64-conda-linux-gnu-cc (GCC) 11.2.0
Copyright (C) 2021 Free Software Foundation, Inc.
This is free software; see the source for copying conditions.  There is NO
warranty; not even for MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.

Currently, the configure script tries to identify GCC by grepping for lowercase gcc, which results in unrecognized vendor. I found the simplest fix to be to also grep for uppercase GCC, although there could be some better ways to do this using some autotools macros.

[devinamatthews]

I made the vendor detection case-insensitive, so this should be fixed now. Thanks for the report.