While Clang presents an almost identical interface to GNU there will be
some differences. Split the compiler information modules to allow
separate rules for Clang. Start by loading the GNU rules but leave a
place to add Clang-specific information.
Since commit 571dc748 (Recognize Clang C and C++ compilers, 2010-05-17)
we recognize Clang C and C++ support. Add Compiler/Clang-ASM.cmake to
enable use of Clang for ASM too. Also teach Assembler test to try Clang
as an assembler.
Suggested-by: Tobias Pape <tobiaspape@gmail.com>