Add two new checks for use in LLVM configuration files:

* FIND_STD_PROGRAM will find a program in the path or using --with options
  and verify that the path/bin/program is executable. Also allows checking
  for include files and libraries. If found, USE_PROGRAM is set, otherwise
  its not set. Also sets PROGRAM_BIN (bin directory), and PROGRAM_DIR (top
  level directory). If headers are found, sets PROGRAM_INC. If libraries
  are found, sets PROGRAM_LIB.
* CHECK_PROGRAM_SANITY can be used to run a program with some option that
  only produces information output and requires no input. If the output
  matches a regular expression, the program passes the sanity check.
  Otherwise, an error occurs.

llvm-svn: 22458