parser: fix asm modifier parse

[kbkpbot]

Fix issue #25070

Output constrains: =r, =&r, +r, +&r,=m,=rm,=@ccl, =*r
Input constrains: r, 0, rm, i, %r, *m

[huly-for-github]

Connected to Huly®: V_0.6-23587

[spytheman]

hm, that does not work with my local tcc 🤔:
./v -cc tcc -no-retry-compilation vlib/v/slow_tests/assembly/asm_test.amd64.v

[spytheman]

=== C compilation error (from /home/delian/v/thirdparty/tcc/tcc.exe): 
cc: /tmp/v_1000/asm_test.amd64.01K26VFD0GKTC5S097ADB5HCSA.tmp.c:8644: 
  error: unknown constraint '*'
=====================================================================

[spytheman]

If you intend to add asm blocks for commonly used modules like math.bits or strconv, please use syntax that tcc can also process, otherwise it will make bootstrapping more difficult, and compilation for many programs a lot slower, due to the retrying and falling back to slower compilers like clang/gcc.

[spytheman]

Excellent work.