[wasm] Import sys/mman.h through CoreFoundation

Importing `wasi_emulated_mman` in Swift code requires the client to
define `_WASI_EMULATED_MMAN`. `@_implementationOnly import` was the only
way to work around this, but it's now declared as unsafe if it's used in
non-resilient moules (even though it's actually safe as long as the
module does not use type layout of the imported module).
The new scoped import feature always requires the transitive clients to
load privately imported modules, so it's not a good fit for this tricky
case where a special macro must be defined before importing the module.

This patch imports `sys/mman.h` through CoreFoundation while defining
`_WASI_EMULATED_MMAN` in the header exposed by modulemap. This way, the
clients don't need to define it.

Author: kateinoigakukun

CoreFoundation/Base.subproj/ForSwiftFoundationOnly.h

@@ -66,6 +66,11 @@
 #include <termios.h>
 #elif TARGET_OS_WASI
 #include <fcntl.h>
+// Define _WASI_EMULATED_MMAN here to use the emulated mman functions in
+// Foundation-side without requiring transitive clients to define it.
+#undef _WASI_EMULATED_MMAN
+#define _WASI_EMULATED_MMAN
+#include <sys/mman.h>
 #elif TARGET_OS_LINUX
 #include <errno.h>
 #include <features.h>

Sources/Foundation/Data.swift

@@ -36,11 +36,6 @@
 @usableFromInline let memcpy = Musl.memcpy
 @usableFromInline let memcmp = Musl.memcmp
 #elseif canImport(WASILibc)
-#if swift(>=6.0)
-private import wasi_emulated_mman
-#else
-import wasi_emulated_mman
-#endif
 @usableFromInline let calloc = WASILibc.calloc
 @usableFromInline let malloc = WASILibc.malloc
 @usableFromInline let free = WASILibc.free

Sources/Foundation/FileHandle.swift

@@ -29,7 +29,6 @@ fileprivate let _write = Musl.write(_:_:_:)
 fileprivate let _close = Musl.close(_:)
 #elseif canImport(WASILibc)
 import WASILibc
-@_implementationOnly import wasi_emulated_mman
 fileprivate let _read = WASILibc.read(_:_:_:)
 fileprivate let _write = WASILibc.write(_:_:_:)
 fileprivate let _close = WASILibc.close(_:)