Add a newlib nano copy of libm.

[configure] fix unexpected operator line 3295

equality of two string is `=` not `==` see `test(1)`

The gamma functions use the reentrant structure which changes size in newlib
nano, so we need a nano specific copy of libm.a to go with libc.a.

Added python3 to Ubuntu prerequisites.

Bump newlib to 3.2.0

Fix non-portable operator in shell conditional

Use = to compare strings with the test builtin command instead of ==,
which is non-standard and sometimes unsupported by stricter POSIX shells
(e.g., dash as /bin/sh).

Add a pr69728 optimization success to the whitelist

I'm not sure what's going on here, but as far as I can tell we're optimizing
this while the test suite thinks we shouldn't be able to.

Signed-off-by: Palmer Dabbelt <palmerdabbelt@google.com>

Don't enable gcc checking by default.

Also, support all gcc checking options instead of just yes and release.
Also, fix copy-and-paste error in cmodel support refering to gcc checking.

Bump gcc to include fix for issue #530.

Add configure options to set target C and C++ compiler flags.

This is a partial fix for pull request #530, allowing people to use
-mno-fdiv for library compiles.

Document Software Collection devtools package for Centos and RHEL.

Bump gcc to including fix for PR91860

Add a Vagrantfile contributed by Dylan McNamee.

Use items rather than iteritems for python 3 compatible

Add macos to travis-ci

Bump gcc

Backport following patches:
- RISC-V: Fix bad insn splits with paradoxical subregs.
- RISC-V: Fix more splitters accidentally calling gen_reg_rtx.
- Fix for PR rtl-optimization/89795

Fix default LINUX_HEADERS_SRCDIR path

The --with-headers argument must point to the `include' subdirectory.

Add option to specify source tree of each component

Fix portability issues

Some implementations of rm(1) are stricter about the ordering of option
and non-option arguments as specified in POSIX.