Fix two issues with the SwiftGlibc module map (swiftlang#32404)

* Fix two issues with the SwiftGlibc module map.

The issues are:

- Today, some submodules in `SwiftGlibc` fail to provide definitions that
  they should contain. As a consequence, Swift fails to import some code
  that compiles correctly with standalone Clang. As just one example,
  including `signal.h` should make the type `pid_t` available, but it
  currently does not.

- `SwiftGlibc` is not compatible with the libc++ module map. Trying to
  include libc++ headers in a C++ module imported into Swift results in an
  error message about cyclic dependencies.

This change fixes both of these issues by making it so that `SwiftGlibc`
no actually longer defines a module map for the glibc headers but merely makes
all of the symbols from those headers available in a module that can be
imported into Swift. C / Objective-C / C++ code, on the other hand, will now
include the glibc headers texually.

For more context on the two issues and this fix, see this forum
discussion:

https://forums.swift.org/t/problems-with-swiftglibc-and-proposed-fix/37594

This change only modifies `glibc.modulemap.gyb` for the time being but
leaves `bionic.modulemap.gyb` and `libc-openbsd.modulemap.gyb` unchanged. The
intent is to fix these in the same way, but it will be easier to do this
in separate PRs that can be tested individually.

Co-authored-by: zoecarver <z.zoelec2@gmail.com>
Co-authored-by: Marcel Hlopko <hlopko@google.com>

Author: 3 people

stdlib/public/Platform/CMakeLists.txt

@@ -119,6 +119,13 @@ foreach(sdk ${SWIFT_SDKS})
       list(APPEND glibc_modulemap_target_list ${copy_glibc_modulemap_static})
     endif()
 
+    set(glibc_header_out "${module_dir}/SwiftGlibc.h")
+    handle_gyb_source_single(glibc_header_target
+        SOURCE "SwiftGlibc.h.gyb"
+        OUTPUT "${glibc_header_out}"
+        FLAGS "-DCMAKE_SDK=${sdk}")
+    list(APPEND glibc_modulemap_target_list ${glibc_header_target})
+
     # If this SDK is a target for a non-native host, except if it's for Android
     # with its own native sysroot, create a native modulemap without a sysroot
     # prefix. This is the one we'll install instead.
@@ -150,11 +157,17 @@ foreach(sdk ${SWIFT_SDKS})
     swift_install_in_component(FILES "${glibc_modulemap_out}"
                                DESTINATION "lib/swift/${arch_subdir}"
                                COMPONENT sdk-overlay)
+    swift_install_in_component(FILES "${glibc_header_out}"
+                               DESTINATION "lib/swift/${arch_subdir}"
+                               COMPONENT sdk-overlay)
 
     if(SWIFT_BUILD_STATIC_STDLIB)
       swift_install_in_component(FILES "${glibc_modulemap_out}"
                                  DESTINATION "lib/swift_static/${arch_subdir}"
                                  COMPONENT sdk-overlay)
+      swift_install_in_component(FILES "${glibc_header_out}"
+                                 DESTINATION "lib/swift_static/${arch_subdir}"
+                                 COMPONENT sdk-overlay)
     endif()
   endforeach()
 endforeach()

stdlib/public/Platform/SwiftGlibc.h.gyb

@@ -0,0 +1,107 @@
+%{
+headers = [
+  'stdc-predef.h',
+  'features.h',
+
+  # C standard library
+  'complex.h',
+  'ctype.h',
+  'errno.h',
+  'fenv.h',
+  'float.h',
+  'inttypes.h',
+  'iso646.h',
+  'libutil.h',
+  'limits.h',
+  'locale.h',
+  'math.h',
+  'pty.h',
+  'setjmp.h',
+  'signal.h',
+  'stdarg.h',
+  'stdbool.h',
+  'stddef.h',
+  'stdint.h',
+  'stdio.h',
+  'stdlib.h',
+  'string.h',
+  'tgmath.h',
+  'time.h',
+  'utmp.h',
+  'utmpx.h',
+
+  # POSIX
+  'aio.h',
+  'arpa/inet.h',
+  'bsd/ifaddrs.h',
+  'bsd/pty.h',
+  'cpio.h',
+  'dirent.h',
+  'dlfcn.h',
+  'fcntl.h',
+  'fmtmsg.h',
+  'fnmatch.h',
+  'ftw.h',
+  'glob.h',
+  'grp.h',
+  'iconv.h',
+  'ifaddrs.h',
+  'langinfo.h',
+  'libgen.h',
+  'link.h',
+  'monetary.h',
+  'net/if.h',
+  'netdb.h',
+  'netinet/in.h',
+  'netinet/tcp.h',
+  'nl_types.h',
+  'poll.h',
+  'pthread.h',
+  'pwd.h',
+  'regex.h',
+  'sched.h',
+  'search.h',
+  'semaphore.h',
+  'spawn.h',
+  'strings.h',
+  'sys/event.h',
+  'sys/file.h',
+  'sys/inotify.h',
+  'sys/ioctl.h',
+  'sys/ipc.h',
+  'sys/mman.h',
+  'sys/msg.h',
+  'sys/resource.h',
+  'sys/select.h',
+  'sys/sem.h',
+  'sys/sendfile.h',
+  'sys/shm.h',
+  'sys/socket.h',
+  'sys/stat.h',
+  'sys/statvfs.h',
+  'sys/time.h',
+  'sys/times.h',
+  'sys/types.h',
+  'sys/uio.h',
+  'sys/un.h',
+  'sys/user.h',
+  'sys/utsname.h',
+  'sys/wait.h',
+  'sysexits.h',
+  'syslog.h',
+  'tar.h',
+  'termios.h',
+  'ulimit.h',
+  'unistd.h',
+  'utime.h',
+  'utmpx.h',
+  'wait.h',
+  'wordexp.h',
+]
+}%
+
+% for header in headers:
+#if __has_include(<${header}>)
+#include <${header}>
+#endif
+% end