Update gcc to 10.1 and turn C++ support on

[PiotrZierhoffer]

These changes update gcc to 10.1 and add C++ support for gcc with newlib.

This addresses #25.

Simply adding c++ to --enable-lanaguages does not work, as libstdc++-v3 compilation fails (example in run#3559265510).

Relevant error

2021-09-09T17:50:07.1357393Z checking for EOWNERDEAD... no
2021-09-09T17:50:07.4128896Z configure: WARNING: uchar.h: present but cannot be compiled
2021-09-09T17:50:07.4131294Z configure: WARNING: uchar.h:     check for missing prerequisite headers?
2021-09-09T17:50:07.4132244Z configure: WARNING: uchar.h: see the Autoconf documentation
2021-09-09T17:50:07.4133308Z configure: WARNING: uchar.h:     section "Present But Cannot Be Compiled"
2021-09-09T17:50:07.4135065Z configure: WARNING: uchar.h: proceeding with the compiler's result
2021-09-09T17:50:07.4752788Z configure: WARNING: sys/ioctl.h: present but cannot be compiled
2021-09-09T17:50:07.4753965Z configure: WARNING: sys/ioctl.h:     check for missing prerequisite headers?
2021-09-09T17:50:07.4754907Z configure: WARNING: sys/ioctl.h: see the Autoconf documentation
2021-09-09T17:50:07.4755833Z configure: WARNING: sys/ioctl.h:     section "Present But Cannot Be Compiled"
2021-09-09T17:50:07.4757419Z configure: WARNING: sys/ioctl.h: proceeding with the compiler's result
2021-09-09T17:50:07.5768378Z configure: WARNING: sys/uio.h: present but cannot be compiled
2021-09-09T17:50:07.5769546Z configure: WARNING: sys/uio.h:     check for missing prerequisite headers?
2021-09-09T17:50:07.5770469Z configure: WARNING: sys/uio.h: see the Autoconf documentation
2021-09-09T17:50:07.5771395Z configure: WARNING: sys/uio.h:     section "Present But Cannot Be Compiled"
2021-09-09T17:50:07.5772939Z configure: WARNING: sys/uio.h: proceeding with the compiler's result
2021-09-09T17:50:07.6197657Z configure: WARNING: fenv.h: present but cannot be compiled
2021-09-09T17:50:07.6198800Z configure: WARNING: fenv.h:     check for missing prerequisite headers?
2021-09-09T17:50:07.6199751Z configure: WARNING: fenv.h: see the Autoconf documentation
2021-09-09T17:50:07.6200656Z configure: WARNING: fenv.h:     section "Present But Cannot Be Compiled"
2021-09-09T17:50:07.6202142Z configure: WARNING: fenv.h: proceeding with the compiler's result
2021-09-09T17:50:07.6947584Z configure: WARNING: stdbool.h: present but cannot be compiled
2021-09-09T17:50:07.6948809Z configure: WARNING: stdbool.h:     check for missing prerequisite headers?
2021-09-09T17:50:07.6949778Z configure: WARNING: stdbool.h: see the Autoconf documentation
2021-09-09T17:50:07.6950705Z configure: WARNING: stdbool.h:     section "Present But Cannot Be Compiled"
2021-09-09T17:50:07.6952214Z configure: WARNING: stdbool.h: proceeding with the compiler's result
2021-09-09T17:50:07.7243875Z configure: WARNING: stdalign.h: present but cannot be compiled
2021-09-09T17:50:07.7244944Z configure: WARNING: stdalign.h:     check for missing prerequisite headers?
2021-09-09T17:50:07.7245921Z configure: WARNING: stdalign.h: see the Autoconf documentation
2021-09-09T17:50:07.7246856Z configure: WARNING: stdalign.h:     section "Present But Cannot Be Compiled"
2021-09-09T17:50:07.7248348Z configure: WARNING: stdalign.h: proceeding with the compiler's result
2021-09-09T17:50:07.7541210Z configure: error: computing EOF failed
2021-09-09T17:50:07.7953876Z make[1]: *** [Makefile:11271: configure-target-libstdc++-v3] Error 1
2021-09-09T17:50:07.7960292Z make: *** [Makefile:954: all] Error 2

Updating --prefix config option helps and fixes compilation process.

Unfortunately it doesn't run properly.

$ riscv32-elf-g++ main.cpp
riscv32-elf-g++: fatal error: cannot read spec file '/home/user/conda/miniconda3/envs/gcc/lib/gcc/': Is a directory
compilation terminated.

$ riscv32-elf-gcc main.cpp
riscv32-elf-gcc: error: main.cpp: C++ compiler not installed on this system

$ riscv32-elf-newlib-g++ main.cpp
riscv32-elf-newlib-g++: fatal error: cannot read spec file '/home/user/conda/miniconda3/envs/gcc/lib/gcc/': Is a directory
compilation terminated.

$ cat main.cpp
#include <iostream>

using namespace std;

int main(){
        cout << "Hello World!" << endl;
        bool x = true;
        return x;
}

conda-build rewrites the internal paths to get rid of the build prefix, but then gcc fails to locate necessary files. We can investigate that further in the next step.

Adding build/detect_binary_files_with_prefix: False value to gcc/newlib/meta.yaml partially fixes the problem.

gcc and g++ work correctly now, but simple strings execution reveals, that paths from build process are still present in the binaries.
It doesn't seem to affect the gcc functionality though.

[PiotrZierhoffer]

FYI @mithro, @tcal-x

[mithro]

It sounds like there is an issue around sysroot -- see https://gcc.gnu.org/onlinedocs/gcc/Directory-Options.html ?

There might be useful information in https://elinux.org/images/1/15/Anatomy_of_Cross-Compilation_Toolchains.pdf and https://www.linuxfromscratch.org/lfs/view/stable/chapter05/glibc.html ?

[mithro]

There is some talk about how libstdc++ and stuff need to be deferred as part of cross compiling at https://www.linuxfromscratch.org/lfs/view/stable/chapter05/gcc-libstdc++-pass1.html

[mithro]

See also https://wiki.osdev.org/GCC_Cross-Compiler

[PiotrZierhoffer]

For some reason the upload hangs, but all other jobs passed. Merging, I suspect a github hiccup here