[libcxx] Capture configuration information when installing the libc++ headers

Summary:
Hi all,

This patch is a successor to D11963. However it has changed dramatically and I felt it would be best to start a new review thread.

Please read the design documentation added in this patch for a description of how it works.

Reviewers: mclow.lists, danalbert, jroelofs, EricWF

Subscribers: vkalintiris, rnk, ed, espositofulvio, asl, eugenis, cfe-commits

Differential Revision: http://reviews.llvm.org/D13407

git-svn-id: https://llvm.org/svn/llvm-project/libcxx/trunk@250235 91177308-0d34-0410-b5e6-96231b3b80d8

include/CMakeLists.txt

@@ -1,10 +1,12 @@
 if (NOT LIBCXX_INSTALL_SUPPORT_HEADERS)
   set(LIBCXX_SUPPORT_HEADER_PATTERN PATTERN "support" EXCLUDE)
 endif()
+
 set(LIBCXX_HEADER_PATTERN
   PATTERN "*"
   PATTERN "CMakeLists.txt" EXCLUDE
   PATTERN ".svn" EXCLUDE
+  PATTERN "__config_site.in" EXCLUDE
   ${LIBCXX_SUPPORT_HEADER_PATTERN}
   )
 
@@ -22,4 +24,29 @@ if (LIBCXX_INSTALL_HEADERS)
     ${LIBCXX_HEADER_PATTERN}
     PERMISSIONS OWNER_READ OWNER_WRITE GROUP_READ WORLD_READ
   )
+
+  if (LIBCXX_NEEDS_SITE_CONFIG)
+    set(UNIX_CAT cat)
+    if (WIN32)
+      set(UNIX_CAT type)
+    endif()
+    # Generate and install a custom __config header. The new header is created
+    # by  prepending __config_site to the current __config header.
+    add_custom_command(OUTPUT ${LIBCXX_BINARY_DIR}/__generated_config
+      COMMAND ${CMAKE_COMMAND} -E copy ${LIBCXX_BINARY_DIR}/__config_site ${LIBCXX_BINARY_DIR}/__generated_config
+      COMMAND ${UNIX_CAT} ${LIBCXX_SOURCE_DIR}/include/__config >> ${LIBCXX_BINARY_DIR}/__generated_config
+      DEPENDS ${LIBCXX_SOURCE_DIR}/include/__config
+              ${LIBCXX_BINARY_DIR}/__config_site
+    )
+    # Add a target that executes the generation commands.
+    add_custom_target(generate_config_header ALL
+      DEPENDS ${LIBCXX_BINARY_DIR}/__generated_config)
+    # Install the generated header as __config.
+    install(FILES ${LIBCXX_BINARY_DIR}/__generated_config
+      DESTINATION include/c++/v1
+      PERMISSIONS OWNER_READ OWNER_WRITE GROUP_READ WORLD_READ
+      RENAME __config
+      COMPONENT libcxx)
+  endif()
+
 endif()

include/__config_site.in

@@ -0,0 +1,20 @@
+//===----------------------------------------------------------------------===//
+//
+//                     The LLVM Compiler Infrastructure
+//
+// This file is dual licensed under the MIT and the University of Illinois Open
+// Source Licenses. See LICENSE.TXT for details.
+//
+//===----------------------------------------------------------------------===//
+
+#ifndef _LIBCPP_CONFIG_SITE
+#define _LIBCPP_CONFIG_SITE
+
+#cmakedefine _LIBCPP_HAS_NO_GLOBAL_FILESYSTEM_NAMESPACE
+#cmakedefine _LIBCPP_HAS_NO_STDIN
+#cmakedefine _LIBCPP_HAS_NO_STDOUT
+#cmakedefine _LIBCPP_HAS_NO_THREADS
+#cmakedefine _LIBCPP_HAS_NO_MONOTONIC_CLOCK
+#cmakedefine _LIBCPP_HAS_NO_THREAD_UNSAFE_C_FUNCTIONS
+
+#endif