Fix #20982 - wrong line number in iasmgcc

[dkorpel]

Still need to test this, the unittest in this module calls parseGccAsm but not gccAsmSemantic.

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Testing this PR locally

If you don't have a local development environment setup, you can use Digger to test this PR:

dub run digger -- build "stable + dmd#20993"

[ibuclaw]

All gdc tests pass with this now.

PASS: gdc.dg/asm1.d    (test for errors, line 37)
PASS: gdc.dg/asm1.d    (test for errors, line 61)
PASS: gdc.dg/asm1.d    (test for errors, line 66)
PASS: gdc.dg/asm1.d    (test for errors, line 73)
PASS: gdc.dg/asm1.d    (test for errors, line 8)
PASS: gdc.dg/asm1.d    (test for errors, line 89)
PASS: gdc.dg/asm1.d    at line 18 (test for errors, line 17)
PASS: gdc.dg/asm1.d    at line 19 (test for errors, line 17)
PASS: gdc.dg/asm1.d    at line 26 (test for errors, line 25)
PASS: gdc.dg/asm1.d    at line 27 (test for errors, line 25)
PASS: gdc.dg/asm1.d    at line 28 (test for errors, line 25)
PASS: gdc.dg/asm1.d    at line 29 (test for errors, line 25)
PASS: gdc.dg/asm1.d    at line 49 (test for errors, line 48)
PASS: gdc.dg/asm1.d    at line 50 (test for errors, line 48)
PASS: gdc.dg/asm1.d   (test for excess errors)

[dkorpel]

Good, since there's no easy way to test this in dmd, let's just merge this.