The definition may be tagged with `extern`, however, this does nothing. In the
header, it may be used to indicate to other TUs that the definition is external
to the TU. Remove the unnecessary modifier. NFC.
errno is implemented as a macro in many environments. The accessor hidden
behind the macro is not a standard function, so we ended up with an
implementation specific handling across all the targets. Shim the function in C
where it can be hidden behind the CPP. This simplifies the implementation on
the swift side.
This adds the swiftMSVCRT module which is similar in spirit to swiftGlibc and
swiftDarwin, exposing the Microsoft C Runtime library to swift. Furthermore,
disable pieces of the standard library which are not immediately trivially
portable to Windows. A lot of this functionality can still be implemented and
exposed to the user, however, this is the quickest means to a PoC for native
windows support.
As a temporary solution, add a -DCYGWIN flag to indicate that we are building
for the cygwin windows target. This allows us to continue supporting the cygwin
environment whilst making the windows port work natively against the windows
environment (msvc). Eventually, that will hopefully be replaced with an
environment check in swift.
The general rule here is that something needs to be SWIFT_CC(swift)
if it's just declared in Swift code using _silgen_name, as opposed to
importing something via a header.
Of course, SWIFT_CC(swift) expands to nothing by default for now, and
I haven't made an effort yet to add the indirect-result / context
parameter ABI attributes. This is just a best-effort first pass.
I also took the opportunity to shift a few files to just implement
their shims header and to demote a few things to be private stdlib
interfaces.
