Swift has some module maps it overlays on Linux and Windows that groups all of the C standard library headers into a single module. This doesn’t allow clang and C++ headers to layer properly with the OS/SDK modules. clang will set -fbuiltin-headers-in-system-modules as necessary for Apple SDKs, but Swift will need to pass that flag itself when required by its module maps.
`module.map` as a module map name has been discouraged since 2014, and
Clang will soon warn on its usage. This patch renames all instances of
`module.map` in the Swift tests to `module.modulemap` in preparation
for this change to Clang.
rdar://106123303
When creating ClangImporter directly from cc1 args, there is no need for
clang path, and it might even be mistaken as an input path. Don't use
clang executable path in the arguments when creating from cc1 commands.
Controlled with a new flag '-direct-clang-cc1-module-build'
This will allow clients to formulate 'swift-frontend' invocations with fully-specified set of cc1 arguments (using '-Xcc -Xclang -Xcc <FLAG>') required for the PCM build, without having to go through the driver.
