Allow an invocation like clang -fmodule-header bar.h (which will be a C++
compilation, but using a header which will be recognised as a C one).
Also we do not want to produce:
"treating 'c-header' input as 'c++-header' when in C++ mode"
diagnostics when the user has been specific about the intent.
Differential Revision: https://reviews.llvm.org/D121590
These command-line flags are alternates to providing the -x
c++-*-header indicators that we are building a header unit.
Act on fmodule-header= for headers on the c/l:
If we have x.hh -fmodule-header, then we should treat that header
as a header unit input (equivalent to -xc++-header-unit-header x.hh).
Likewise, for fmodule-header={user,system} the source should be now
recognised as a header unit input (since this can affect the job list
that we need).
It's not practical to recognise a header without any suffix so
-fmodule-header=system foo isn't going to happen. Although
-fmodule-header=system foo.hh will work OK. However we can make it
work if the user indicates that the item without a suffix is a valid
header. (so -fmodule-header=system -xc++-header vector)
Differential Revision: https://reviews.llvm.org/D121589
Iain Sandoe