Bump binutils to support CSR checking and Zv* sub extensions for rvv.

Bump riscv-gcc and riscv-binutils to support rvv-0.9.x

Bump riscv-gcc to riscv-gcc-9.2.0-rvv, and bump binutils to support the
rvv constraints checking options.

This testcase is used to check whether the linker is work normally when both
the --wrap=SYMBOL and -flto are set.  It seems that the current fix only can
work when the wrapped symbol `SYMBOL` is defined in the other files and will be
linked.  See the pr-24406-1 test, the `read` symbol is defined in the glibc’s
libc.so.6, and we will also link the libc.so.6 by the linux toolchain, so it
works.  But the `read` symbol isn’t defined in the newlib, or other linked
objects or archives.  Therefore, the pr-24406-1 testsuite is always failed
for riscv elf toolchain, but seems to work for riscv linux toolchain.

On the other hand, if the wrapped symbol is `read_p`, it isn't defined in the
other linked files, so we also get the error link for the linux toolchain.
The fix in upstream seems not complete.  I suppose that we shoud just skip the
pr-24406-1 testcase until upstream fix or remove it.

Update binutils to version 0.8-draft-20191207.

This should be the last update for version 0.8-draft.
Please see the details as follows:

* Support limited vector load/store and move whole register.
* Accept constant 0 for address of vector amo instruction.
* Support the vector instruction constraints.

Update binutils for the syntax of vamo.

Bump binutils to riscv-binutils-2.33.1-rvv-0.8.x

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.

These wrappers are still necessary on non-GNU platforms; glibc
makefile rules invoke `sed' directly with GNU extensions.

Check write permission to install path before build anything

Clean up rules for patch source, it's no longer used after using submodule

Document problems with using same prefix for more than one build.

Increase the timeout for git command.