rv64 inline assembly support

[raw-bin]

Please consider this PR that:

1. Adds support for parsing rv64 inline assembly

2. Adds a local test runner specifiable via the following comments in the test file (for example):
   // vtest vflags: -cc riscv64-linux-gnu-gcc -gc none
   // vtest runner: qemu-riscv64
   // vtest runner_flags: -L /usr/riscv64-linux-gnu

   The runner invocation in the above example assumes that the qemu-user package is installed on the host system.

3. Adds support for parsing rv64 inline assembly using the following addressing modes:

   • displacement from base register (eg: sd a0, 0(a1))
   • composite displacement from base register (eg: sd a0, (8 * 1)(a1))

4. Adds a test for those new addressing modes

Note that I have run the following successfully:

• make check
• v vlib/v/gen/c/coutput_test.v

[huly-for-github]

Connected to Huly®: V_0.6-22684

[medvednikov]

FAIL [ 530/2359] C: 1298.4 ms, R: 58504.996 ms vlib/v/gen/c/coutput_test.v