Bring some sanity here. Feel free to specify parameters in any order and in any notation (full name or one-letter).
# Load LLVM/Clang
if (CLANG)
set(CLANG_EXECUTABLE ${CLANG})
else()
find_program(CLANG_EXECUTABLE
NAMES clang-mp-3.3 clang-mp-3.2 clang-mp-3.1 clang-mp-3.0 clang
PATHS /opt/local/bin /usr/local/bin /usr/bin)
endif()
# Check LLVM/Clang version
if (CLANG_EXECUTABLE)
exec_program(${CLANG_EXECUTABLE} ARGS "-v" OUTPUT_VARIABLE CLANG_VERSION_FULL)
string(REGEX MATCH "[0-9]+\\.[0-9]+" CLANG_VERSION_LONG "${CLANG_VERSION_FULL}")
string(REGEX REPLACE "([0-9]+\\.[0-9]+)" "\\1" CLANG_VERSION "${CLANG_VERSION_LONG}")
else()
message(FATAL_ERROR "No LLVM/Clang compiler found (required for engine_c target)")
endif()
set(CMAKE_C_COMPILER ${CLANG_EXECUTABLE})