[c] Update the C grammar to the latest ISO Spec, and fixing various issues.

[kaby76]

NB: This PR is still in progress. I am currently debugging the gcc compiler (actually cc1) to understand the parser flow and the grammar it implements, specifically for the gcc extensions. The old gcc extensions currently in the c grammar are incorrect.

This PR brings the C grammar up to date with the latest ISO Specification. It also fixes several critical bugs in the correctness of the parse with respect to types.

As noted in several reported Issues for c, several examples were parsed incorrectly. This was because the EBNF in the ISO Specification, which this grammar is based on, is ambiguous. To disambiguate the grammar, I added a symbol table to the grammar's actions.

At this point, any C code input must be pre-processed so that any and all definitions are included in the input. The parser must have this information to perform type checking and select the correct parse.

Fixed

• [C] declarationSpecifiers is too greedy, take initDeclaratorList as typedefName #4676
• [C] struct members are parsed as typedefs #1979
• [c] Cannot parse 'typedef struct {} x;' #4683
• [c] C grammar really should have a basic symbol table. #4380
• https://groups.google.com/g/antlr-discussion/c/nGvUxmnOxsI
• Fixed illegal C input examples.
• Added parse tree validation checks with .trq files.
• Fix supercedes Update C.g4 #3933 and Create StructOrUnionSpecifier.c #3934

Already fixed. Please close.

• [C] Error "no viable alternative" for function returning pointer type. #1065
• [C] function pointer cannot be handled by the C grammar. #1066
• [ANTLR4][C] Function call with single argument should be recognized as statement but actually declaration. #1082
• c: unable to parse FunctionPointer.c #1115

[kaby76]

BS! Some of the examples in the test suite are not strict ISO C. For example, this should not parse.

int p1, p2;
int a2(int param1, param2);

But, it does!

$ gcc -c -std=c24 p.c
gcc.exe: error: unrecognized command-line option '-std=c24'; did you mean '-std=c2x'?
11/22-08:50:09 ~/issues/g4-current/c/Generated-CSharp
$ gcc -c -std=c2x p.c
p.c:2:20: error: unknown type name 'param2'
    2 | int a2(int param1, param2);
      |                    ^~~~~~
11/22-08:50:17 ~/issues/g4-current/c/Generated-CSharp
$ cat p.c
int p1, p2;
int a2(int param1, param2);
11/22-08:51:49 ~/issues/g4-current/c/Generated-CSharp
$ ./bin/Debug/net8.0/Test.exe p.c
CSharp 0 p.c success 0.0453763
Total Time: 0.1107057
11/22-08:52:29 ~/issues/g4-current/c/Generated-CSharp
$

It can't parse because a declarator must include a type, as with int param2. int param1, param2 currently parses because param2 is parsed as a type id, as though you were give it int param1, int. We cannot at the same time ignore this, and add a symbol table to solve #4676.

So, several of the examples provided should not parse, but they do.