INSTALLING 64-BIT CLANG 13.0.0
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Jan 23, 2022 
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1. Download llvm-mingw-20211002-msvcrt-x86_64.zip from Martin Storsjo's Github respository(104 MB).

2. Extract to D:\ (example) like so:

        d:\llvm-mingw-20211002-msvcrt-x86_64
           +- include
           +- lib
           +- bin
           +- aarch64-w64-mingw32
           +- i686-w64-mingw32
           +- armv7-w64-mingw32
           +- x86_64-w64-mingw32

3. Script to set environment/path.

    @echo off
    set CLANG=d:\llvm-mingw-20211002-msvcrt-x86_64
    set MYINCLUDE=d:\my_include
    set MYLIB=d:\my_lib
    set archtype=64
    repath -u c:\llvm* -u d:\llvm* -u c:\mingw* -u d:\mingw* -e %CLANG%\bin
    call _repath.bat
    del _repath.bat
    set c_include_dir=%MYINCLUDE%
    set c_include_path=%MYINCLUDE%;%CLANG%\lib\clang\13.0.0\include;%CLANG%\include
    set cplus_include_path=%MYINCLUDE%;%CLANG%\include\c++\v1;%CLANG%\lib\clang\13.0.0\include;%CLANG%\include
    set library_path=%MYLIB%;%CLANG%\lib\clang\13.0.0\lib\windows;%CLANG%\lib;%CLANG%\x86_64-w64-mingw32\lib
    set libdir=
    set exedir=c:\bin%archtype%
    set cc=gcc
    set cpp=g++
    set f77=g77
    set cflags=-Ofast -Wall -m64
    %cc% -v