llvm: Raise SkipRecipe exception for unsupported architectures
When parsing this recipe on an unsupported or non-mappable architecture
an error is generated despite no dependencies on the recipe. E.g.
ERROR: .../llvm_git.bb: cannot map 'microblazeel' to a supported llvm architecture
Instead of generating an error which might confuse users, raise a
SkipRecipe exception similar to other arch-style mapping functions (e.g.
go_map_arch). This avoids showing the error during parse, and prevents
the use of the recipe on unsupported targets. Resulting in an error like
so when trying to build llvm:
ERROR: Nothing PROVIDES 'llvm'
llvm was skipped: Cannot map 'microblazeel' to a supported LLVM architecture
Signed-off-by: Nathan Rossi <nathan@nathanrossi.com> Signed-off-by: Ross Burton <ross.burton@intel.com>
