gollvm compiler support

[kmlebedev]

This is necessary to native support the e2k platform with all the necessary optimizations for VLIW.

1. Build gollvm

% mkdir workarea
% cd workarea

// Sources
% git clone https://github.com/llvm/llvm-project.git
...
% cd llvm-project/llvm/tools
% git clone https://go.googlesource.com/gollvm
...
% cd gollvm
% git clone https://go.googlesource.com/gofrontend
...
% cd libgo
% git clone https://github.com/libffi/libffi.git
...
% git clone https://github.com/ianlancetaylor/libbacktrace.git
...
%

3. Codegen llvm-ir

% go build -work -x mypackage.go 1> transcript.txt 2>&1
% egrep '(WORK=|llvm-goc -c)' transcript.txt
WORK=/tmp/go-build887931787
/t/bin/llvm-goc -c -g -m64 -fdebug-prefix-map=$WORK=/tmp/go-build \
  -gno-record-gcc-switches -fgo-pkgpath=command-line-arguments \
  -fgo-relative-import-path=/mygopath/src/tmp -o $WORK/b001/_go_.o \
  -I $WORK/b001/_importcfgroot_ ./mypackage.go
% /t/bin/llvm-goc -c -g -m64 -fdebug-prefix-map=$WORK=/tmp/go-build \
  -gno-record-gcc-switches -fgo-pkgpath=command-line-arguments \
  -fgo-relative-import-path=/mygopath/src/tmp \
  -I $WORK/b001/_importcfgroot_ -o mypackage.ll -S -emit-llvm \
  ./mypackage.go

4. Compile llvm with llc

/usr/lib/llvm-13/bin/llc -mtriple=e2k64-unknown-linux-gnu file.ll -O3 --filetype=obj