Update newlib and libc++ build scripts and artifacts

[bradjc]

This will eventually remove the need for installing newlib.

• compile libc++ for riscv
• update newlib
• provide newlib headers
• compile libc++ for individual arm targets
• rename variable in configuration (no longer legacy)
• use provided libc++ for riscv (not system)
• bundle all artifacts in some sort of zip file and host on multiple servers
• update make system to download those artifacts as needed
• remove artifacts from this repo
• namespace artifacts so we could easily add support for picolibc if we wanted to
• update CI to use recent toolchains and OSes

[bradjc]

Arg I can't even test this. With the new homebrew mac arm-none-eabi-gcc:

$  arm-none-eabi-gcc --print-multi-lib
.;
thumb;@mthumb
arm/autofp/v5te/fpu;@marm@mfpu=auto@march=armv5te+fp@mfloat-abi=hard
thumb/autofp/v7/fpu;@mthumb@mfpu=auto@march=armv7+fp@mfloat-abi=hard

So those are the only multilib versions that newlib builds.

Here is the homebrew formula: https://github.com/Homebrew/homebrew-core/blob/master/Formula/a/arm-none-eabi-gcc.rb. It isn't clear to me why those are the multilib targets for the toolchain.

[bradjc]

Compared to the latest version here: https://developer.arm.com/downloads/-/arm-gnu-toolchain-downloads

$  ./arm-none-eabi-gcc --print-multi-lib
.;
arm/v5te/softfp;@marm@march=armv5te+fp@mfloat-abi=softfp
arm/v5te/hard;@marm@march=armv5te+fp@mfloat-abi=hard
thumb/nofp;@mthumb@mfloat-abi=soft
thumb/v7/nofp;@mthumb@march=armv7@mfloat-abi=soft
thumb/v7+fp/softfp;@mthumb@march=armv7+fp@mfloat-abi=softfp
thumb/v7+fp/hard;@mthumb@march=armv7+fp@mfloat-abi=hard
thumb/v7-r+fp.sp/softfp;@mthumb@march=armv7-r+fp.sp@mfloat-abi=softfp
thumb/v7-r+fp.sp/hard;@mthumb@march=armv7-r+fp.sp@mfloat-abi=hard
thumb/v7-a/nofp;@mthumb@march=armv7-a@mfloat-abi=soft
thumb/v7-a+fp/softfp;@mthumb@march=armv7-a+fp@mfloat-abi=softfp
thumb/v7-a+fp/hard;@mthumb@march=armv7-a+fp@mfloat-abi=hard
thumb/v7-a+simd/softfp;@mthumb@march=armv7-a+simd@mfloat-abi=softfp
thumb/v7-a+simd/hard;@mthumb@march=armv7-a+simd@mfloat-abi=hard
thumb/v7ve+simd/softfp;@mthumb@march=armv7ve+simd@mfloat-abi=softfp
thumb/v7ve+simd/hard;@mthumb@march=armv7ve+simd@mfloat-abi=hard
thumb/v8-a/nofp;@mthumb@march=armv8-a@mfloat-abi=soft
thumb/v8-a+simd/softfp;@mthumb@march=armv8-a+simd@mfloat-abi=softfp
thumb/v8-a+simd/hard;@mthumb@march=armv8-a+simd@mfloat-abi=hard
thumb/v6-m/nofp;@mthumb@march=armv6s-m@mfloat-abi=soft
thumb/v7-m/nofp;@mthumb@march=armv7-m@mfloat-abi=soft
thumb/v7e-m/nofp;@mthumb@march=armv7e-m@mfloat-abi=soft
thumb/v7e-m+fp/softfp;@mthumb@march=armv7e-m+fp@mfloat-abi=softfp
thumb/v7e-m+fp/hard;@mthumb@march=armv7e-m+fp@mfloat-abi=hard
thumb/v7e-m+dp/softfp;@mthumb@march=armv7e-m+fp.dp@mfloat-abi=softfp
thumb/v7e-m+dp/hard;@mthumb@march=armv7e-m+fp.dp@mfloat-abi=hard
thumb/v8-m.base/nofp;@mthumb@march=armv8-m.base@mfloat-abi=soft
thumb/v8-m.main/nofp;@mthumb@march=armv8-m.main@mfloat-abi=soft
thumb/v8-m.main+fp/softfp;@mthumb@march=armv8-m.main+fp@mfloat-abi=softfp
thumb/v8-m.main+fp/hard;@mthumb@march=armv8-m.main+fp@mfloat-abi=hard
thumb/v8-m.main+dp/softfp;@mthumb@march=armv8-m.main+fp.dp@mfloat-abi=softfp
thumb/v8-m.main+dp/hard;@mthumb@march=armv8-m.main+fp.dp@mfloat-abi=hard
thumb/v8.1-m.main+mve/hard;@mthumb@march=armv8.1-m.main+mve@mfloat-abi=hard

[bradjc]

Testing the newlib script on a new checkout worked for me.

[bradjc]

Still a lot to cleanup, but I've made some progress on packaging the compiled libraries into a zip which can be fetched via zip.

This PR will certainly need to be rebased to remove the commits which add all the artifacts.

[bradjc]

Replaced by #353