Allow compiling with clang/clang++ without manual patching.
Allow compiling with clang/clang++ without manual patching.

As a side effect, the configure script will now find clang before gcc.
In the (presumably not very common) case of building on a Linux system
that has clang, the following can be used to force use of gcc:

  ./configure CC=gcc CXX=g++

git-svn-id: 03a8048b5ee8463be5048a3801110fb50f378627@12468 d0ab736e-dc22-4aeb-8dc9-08def0aa14fd

kmdouglass/Micro-Manager,kmdouglass/Micro-Manager