title: valgrind/yosemite installation fails "configure"; clang not recognized
body: <p>A previous installation of valgrind had succeeded but was deleted (by "rm -rf' of every "valgrind" directory found). Reinstallation now fails at the "./configure --prefix=/usr/local" step with the following error message:</p>
  
  <p>".. checking for diff -u... yes
  checking for a supported version of gcc... Configured with: --prefix=/Library/Developer/CommandLineTools/usr --with-gxx-include-dir=/usr/include/c++/4.2.1
  Configured with: --prefix=/Library/Developer/CommandLineTools/usr --with-gxx-include-dir=/usr/include/c++/4.2.1
  no (6.1.0)
  configure: error: please use gcc >= 3.0 or clang >= 2.9 or icc >= 13.0
  Richards-MacBook-Air:valgrind richardcramer$"</p>
  
  <p>Here is the compiler situation:</p>
  
  <p>"Richards-MacBook-Air:usr richardcramer$ clang --version
  Apple LLVM version 6.1.0 (clang-602.0.53) (based on LLVM 3.6.0svn)
  Target: x86_64-apple-darwin14.1.0
  Thread model: posix
  Richards-MacBook-Air:usr richardcramer$"</p>