Fix #21619 - ICE core.exception.AssertError@src/dmd/pragmasem.d(456): Assertion failure

[ibuclaw]

pragma(mangle) in a declaration and statement context had two diverging semantics, and in some cases differing error messages for the same kind of invalid case.

This change merges the two implementation together into one function so that semantic is consistently applied.

[dlang-bot]

Thanks for your pull request, @ibuclaw!

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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#21624"

[ibuclaw]

Needs loads of tests, as I lost count of so many examples where pragma(mangle) violated the spec.

// second argument ignored - spec says one must be symbol
pragma(mangle, "name", "eman")
struct S {}

// second argument also ignored - spec says there must be one argument only
pragma(mangle, "name", "eman")
S fun() { return S(); }

// accepts call expr with return type aggregate - this is neither a string literal nor type symbol
pragma(mangle, fun(), "name")
class C {}

// likewise, accepts var expression of type aggregate
S var;
pragma(mangle, var, "name")
class D {}

// ignored aggregate declarations wrapped around an attribute declaration
pragma(mangle, "function")
extern(C++) struct _function {}
extern(C++) void cppfun(ref _function);  // mangled as `_function&`, not `function&`.

[ibuclaw]

This isn't related. Failure was introduced by e33c664.