# In a msys2/mingw64 command prompt:

mkdir -p /c/code/gcc-bootstrap
cd /c/code/gcc-bootstrap

# Building the new gcc and its sysroot using the existing msys2/mingw64
# gcc installation:
# $ which gcc
# /mingw64/bin/gcc
# $ gcc --version
# gcc.exe (Rev2, Built by MSYS2 project) 7.3.0

export TOOLCHAIN_PREFIX=/c/code/mingw-native
export TARGET_TRIPLET=x86_64-w64-mingw32

# Build libraries that GCC needs. These can also potentially be found
# from the msys2/mingw64 installation, and that should probably also
# work just as well. If omitted, leave out the --with-gmp=$DEPENDS_PREFIX
# from the gcc configure command.

export DEPENDS_PREFIX=/c/code/gcc-depends

wget http://ftp.funet.fi/pub/gnu/gnu/gmp/gmp-6.1.2.tar.bz2
tar -jxvf gmp-6.1.2.tar.bz2
cd gmp-6.1.2
./configure --prefix=$DEPENDS_PREFIX --disable-shared
make -j$(nproc)
make install
cd ..

wget http://ftp.funet.fi/pub/gnu/gnu/mpfr/mpfr-4.0.2.tar.bz2
tar -jxvf mpfr-4.0.2.tar.bz2
cd mpfr-4.0.2
./configure --prefix=$DEPENDS_PREFIX --with-gmp=$DEPENDS_PREFIX --disable-shared
make -j$(nproc)
make install
cd ..

wget http://www.multiprecision.org/downloads/mpc-1.1.0.tar.gz
tar -zxvf mpc-1.1.0.tar.gz
cd mpc-1.1.0
./configure --prefix=$DEPENDS_PREFIX --with-gmp=$DEPENDS_PREFIX --disable-shared
make -j$(nproc)
make install
cd ..

# End of optional section.

wget http://ftp.funet.fi/pub/gnu/gnu/binutils/binutils-2.32.tar.bz2
tar -jxvf binutils-2.32.tar.bz2
cd binutils-2.32
mkdir build
cd build
../configure --prefix=$TOOLCHAIN_PREFIX --disable-werror --disable-multilib
make -j$(nproc)
make install-strip
cd ../..

# Clone mingw-w64; using a recent known-good version from the master branch.
# The v6.x branch should also probably be good for ucrt, but the master branch
# is certainly good at least.
git clone git://git.code.sf.net/p/mingw-w64/mingw-w64
cd mingw-w64
git checkout 69af6ee195e65a29acc02a49119a833606424a1b
cd mingw-w64-headers
mkdir build
cd build
../configure --prefix=$TOOLCHAIN_PREFIX/$TARGET_TRIPLET --with-default-msvcrt=ucrt
make install
cd ../../..

# Build GCC; build the compiler itself and all tools, using the existing
# msys2/mingw64 compiler, having that compiler itself link against the
# CRT that it defaults to. This compiler will be set up that the code
# it produces uses UCRT though.

# Build the same version of gcc as in the surrounding host environment.
# This seems to be necessary for building the Ada tools this particular
# way (a single-stage, non-bootstrap build), as the Ada tools are built
# with the existing host Ada compiler, and the GCC Ada sources are picky
# about being built with the exact right version of the compiler.
wget http://ftp.funet.fi/pub/gnu/gnu/gcc/gcc-7.3.0/gcc-7.3.0.tar.xz
tar -Jxvf gcc-7.3.0.tar.xz
cd gcc-7.3.0 && \
mkdir build
cd build
../configure --prefix=$TOOLCHAIN_PREFIX --enable-languages=c,c++,ada --disable-multilib --with-gmp=$DEPENDS_PREFIX --with-native-system-header-dir=$TOOLCHAIN_PREFIX/$TARGET_TRIPLET/include --disable-bootstrap CXXFLAGS="-O2"
make -j$(nproc) all-gcc
make install-strip-gcc
cd ../..

# Now build the CRT runtimes using the newly built C/C++ compiler.
# Add the new toolchain/compiler to the PATH.

export PATH=$TOOLCHAIN_PREFIX/bin:$PATH

# $ which gcc
# /c/code/mingw-native/bin/gcc
# $ gcc --version
# gcc.exe (GCC) 7.3.0


cd mingw-w64/mingw-w64-crt
mkdir build
cd build
../configure --prefix=$TOOLCHAIN_PREFIX/$TARGET_TRIPLET --disable-lib32 --enable-lib64 --with-default-msvcrt=ucrt
make -j$(nproc)
make install
cd ../../..

# Build the libgcc/libstdc++ runtimes, with the new toolchain and its
# new sysroot (defaulting to UCRT).
cd gcc-7.3.0/build
make -j$(nproc) all-target
make install-target

# Build the rest of the gnat frontend tools using the old host ada compiler:
export PATH=/mingw64/bin:$PATH
make configure-gnattools
cd gnattools
make -j$(nproc) gnattools-cross
cd ..
make install-strip-gcc
cd ../../..

# Copy a few runtime dlls that the compiler ended up requiring.
cp /mingw64/bin/libiconv-2.dll $TOOLCHAIN_PREFIX/bin
cp /mingw64/bin/libwinpthread-1.dll $TOOLCHAIN_PREFIX/bin
cp /mingw64/bin/libgmp-10.dll $TOOLCHAIN_PREFIX/bin