chromium: Switch to using libc++ and compiler_rt in target builds.

This follows what upstream has done in its official builds for years. We had
already been using clang in our builds, but with libstdc++. This has
occasionally caused a number of build issues over the years (e.g. #482), so
it makes sense to just follow upstream's toolchain choices more closely.

Due to kraj/meta-clang#449 the native parts of the
build are still using libstdc++ though, so not all libstdc++-related patches
could be removed in this commit.

This change has been tested exhaustively by multiple people as reported in
the bug below. Big thanks to @kraj, @msisov, @MastaG and @r1mikey for their
testing!

Fixes #488.

Author: Raphael Kubo da Costa

meta-chromium/recipes-browser/chromium/chromium-gn.inc

@@ -15,13 +15,10 @@ SRC_URI += " \
     file://0004-BUILD-do-not-specify-march-on-arm.patch \
     file://0005-Consider-armv7ve-define.patch \
     file://0006-Delete-compiler-options-not-available-in-release-ver.patch \
-    file://0007-Move-CharAllocator-definition-to-a-header-file.patch \
     file://0008-Fix-sandbox-Aw-snap-for-syscalls-403-and-407.patch \
     file://0009-RandBytes-Stop-including-sys-random.h-on-Linux.patch \
     file://0010-avoid-link-latomic-failure-on-CentOS-8-host.patch \
     file://0011-Fix-use-of-DCHECK-with-std-unique_ptr.patch \
-    file://0012-IWYU-add-ctime-for-std-time.patch \
-    file://0013-mojo-Include-string.h-for-strncpy-declaration.patch \
 "
 
 SRC_URI_append_libc-musl = "\

meta-chromium/recipes-browser/chromium/chromium.inc

@@ -18,6 +18,12 @@ TOOLCHAIN = "clang"
 # to build the native recipes (e.g. GN) with clang too.
 TOOLCHAIN_class-native = "clang"
 
+# This makes the target build use libc++ and compiler_rt instead of the GNU
+# runtime, just like upstream does. The native binaries compiled and run as
+# part of the build still use libstdc++ and libgcc though (see
+# https://github.com/kraj/meta-clang/issues/449).
+RUNTIME = "llvm"
+
 inherit mime-xdg pythonnative
 DEPENDS += "python-setuptools-native"