This adds an extension warning when using the preprocessor conditionals
in a language mode they're not officially supported in, and an opt-in
warning for compatibility with previous standards.
Fixes#55306
Differential Revision: https://reviews.llvm.org/D125178
WG14 adopted N2645 and WG21 EWG has accepted P2334 in principle (still
subject to full EWG vote + CWG review + plenary vote), which add
support for #elifdef as shorthand for #elif defined and #elifndef as
shorthand for #elif !defined. This patch adds support for the new
preprocessor directives.
- This is designed to make it obvious that %clang_cc1 is a "test variable"
which is substituted. It is '%clang_cc1' instead of '%clang -cc1' because it
can be useful to redefine what gets run as 'clang -cc1' (for example, to set
a default target).
llvm-svn: 91446
Ken Matsui