Update to the latest version of libcxx

This version can do without the two patches we carried locally.

patches/libcxx-0001.patch

@@ -1,26 +0,0 @@
-From f12a5570d2d24b147122d7b64fc1dadf7226db2c Mon Sep 17 00:00:00 2001
-From: Martin Storsjo <martin@martin.st>
-Date: Fri, 25 Aug 2017 11:00:37 +0300
-Subject: [PATCH 1/2] Handle object files named *.obj in merge_archives.py
-
-Differential Revision: https://reviews.llvm.org/D37133
----
- utils/merge_archives.py | 2 ++
- 1 file changed, 2 insertions(+)
-
-diff --git a/utils/merge_archives.py b/utils/merge_archives.py
-index 856dd3b..b1bd3cb 100755
---- a/utils/merge_archives.py
-+++ b/utils/merge_archives.py
-@@ -120,6 +120,8 @@ def main():
- 
-     files = glob.glob(os.path.join(temp_directory_root, '*.o'))
-     if not files:
-+        files = glob.glob(os.path.join(temp_directory_root, '*.obj'))
-+    if not files:
-         print_and_exit('Failed to glob for %s' % glob_path)
-     cmd = [ar_exe, '-qc', args.output] + files
-     execute_command_verbose(cmd, cwd=temp_directory_root, verbose=args.verbose)
--- 
-2.7.4
-

patches/libcxx-0002.patch

@@ -1,30 +0,0 @@
-From 79a72b66ba63b97812b8f0076c032da9a0033e9e Mon Sep 17 00:00:00 2001
-From: Martin Storsjo <martin@martin.st>
-Date: Fri, 25 Aug 2017 11:06:31 +0300
-Subject: [PATCH 2/2] Rerun ranlib manually after merging the static libraries
-
-In cross build setups, the ar used in merge_archives.py might
-not be the right one for the target; make sure to rebuild the
-index for the static library.
-
-Differential Revision: https://reviews.llvm.org/D37134
----
- lib/CMakeLists.txt | 2 ++
- 1 file changed, 2 insertions(+)
-
-diff --git a/lib/CMakeLists.txt b/lib/CMakeLists.txt
-index 5786514..56b9a22 100644
---- a/lib/CMakeLists.txt
-+++ b/lib/CMakeLists.txt
-@@ -272,6 +272,8 @@ if (LIBCXX_ENABLE_STATIC)
-       "$<TARGET_LINKER_FILE:cxx_static>"
-       "${MERGE_ARCHIVES_ABI_TARGET}"
-       "${MERGE_ARCHIVES_SEARCH_PATHS}"
-+    COMMAND
-+      ${CMAKE_RANLIB} $<TARGET_LINKER_FILE:cxx_static>
-     WORKING_DIRECTORY ${LIBCXX_BUILD_DIR}
-     )
-   endif()
--- 
-2.7.4
-