commit 2d674b68b6d7c1d15de37aec691f2d5afa0dd14f
author Ryan Prichard <rprichard@google.com> Mon Oct 16 23:13:32 2023 -0700
committer Ryan Prichard <rprichard@google.com> Thu Apr 11 16:05:42 2024 -0700
tree dfb7382f9288fb0fc0c1d22f1f3a2512a32f82f8
parent 26b0add08447e578779d9da9d13244b62e1a4a56

Switch to the libc++ toolchain prebuilt

Android currently uses external/libcxx and external/libcxxabi for its
libc++ STL, but these repositories haven't been updated since January
2019. Instead, build libc++ as part of the Android Clang build, and use
a prebuilt libc++ for device and host Soong builds.

The Clang prebuilt already had Soong modules, "libc++_host" and
"libc++abi_host", that imported libc++[abi].{so,dylib} for Darwin+Linux
host only. The clang-tools (e.g. vndk/tools/header-checker, versioner)
need to link against the LLVM prebuilt (e.g. libclang-cpp.so), so they
also must use the newer libc++.so that libclang-cpp.so uses. Generalize
these imports by renaming the llvm_host_prebuilt_library_shared Soong
module type to llvm_prebuilt_library_shared, and renaming the modules:

 * libc++_host --> libc++
 * libc++abi_host --> libc++abi_shared

Avoid renaming the ABI module to just "libc++abi" because the old
external/libcxxabi also defined a "libc++abi" module, but it was a
static library instead. Add a new "libc++abi_static" module. It isn't
clear if these ABI modules are really needed, though. The old
"libc++abi" didn't appear used anywhere in Android's bp/mk files, and
the libc++abi object files are exported from libc++[_static]. The ABI
modules are now host-only, but it may be sensible to remove them
altogether.

Soong also has an NDK libc++ (in prebuilts/ndk/Android.bp), which will
be switched later to the Clang prebuilt.

Previously, the LLVM_BUILD_HOST_TOOLS environment variable set
"enabled" to false for both llvm_host_prebuilt_library_shared (e.g.
libc++_host) and the llvm_host_defaults module (i.e. clang-tools), but
now it only affects the latter. This environment variable can probably
be removed entirely eventually, leaving the clang-tools modules enabled
unconditionally.

Bug: http://b/332594828
Test: treehugger
Change-Id: I78714516f2734e7bc8d0e80e71cd62bc8113a365