[libcxxabi] Import 'libcxxabi-12.0.0' and remove unnecessary files

https://github.com/llvm/llvm-project/releases/llvmorg-12.0.0

See .gitignore for removed files

.gitignore

@@ -42,6 +42,10 @@ out/
 !/llvm/lib/Target/ARM/**
 !/llvm/lib/Target/**/LLVMBuild.txt
 
+### libcxxabi
+# Libcxxabi tests
+/libcxxabi/test/
+
 ### Clang
 # Clang tests
 /clang/test/
@@ -90,4 +94,4 @@ __pycache__/
 /cmake/wimal
 
 ### clangd
-/.cache
+/.cache

libcxxabi/.clang-format

@@ -0,0 +1,12 @@
+BasedOnStyle: LLVM
+
+---
+Language: Cpp
+
+AlwaysBreakTemplateDeclarations: true
+PointerAlignment: Left
+
+# Disable formatting options which may break tests.
+SortIncludes: false
+ReflowComments: false
+---

libcxxabi/.gitignore

@@ -0,0 +1,58 @@
+# Byte-compiled / optimized / DLL files
+__pycache__/
+*.py[cod]
+
+# vim swap files
+.*.sw?
+.sw?
+
+# C extensions
+*.so
+
+# Distribution / packaging
+.Python
+env/
+build/
+develop-eggs/
+dist/
+downloads/
+eggs/
+#lib/ # We actually have things checked in to lib/
+lib64/
+parts/
+sdist/
+var/
+*.egg-info/
+.installed.cfg
+*.egg
+
+# PyInstaller
+#  Usually these files are written by a python script from a template
+#  before PyInstaller builds the exe, so as to inject date/other infos into it.
+*.manifest
+*.spec
+
+# Installer logs
+pip-log.txt
+pip-delete-this-directory.txt
+
+# Unit test / coverage reports
+htmlcov/
+.tox/
+.coverage
+.cache
+nosetests.xml
+coverage.xml
+
+# Translations
+*.mo
+*.pot
+
+# Django stuff:
+*.log
+
+# Sphinx documentation
+docs/_build/
+
+# PyBuilder
+target/