fix Issue 23037 - importC: type with only type-qualifier doesn't work

[WalterBright]

No description provided.

[dlang-bot]

Thanks for your pull request, @WalterBright!

Bugzilla references

Auto-close	Bugzilla	Severity	Description
✓	23037	minor	importC: type with only type-qualifier doesn't work

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#14018"

[huglovefan]

there are still some cases left (some more important than others)

void fn1(const); // segfaults
struct { const : 1; } s1; // asserts
struct { const x; } s2; // silently accepted

void fn2(const x) {} // tries to use "x" as the type for an unnamed parameter
struct { const x : 1; } s3; // tries to use "x" as the base type for an unnamed bit field

// syntax error (doesn't mention the missing type-specifier)
const fn3();
const arr[1];

i didn't expect this would need separate fixes for each case, there might still be some left that i didn't think of (but this should already be most of the common ones)

[WalterBright]

@huglovefan addressed the points you raised.