cgen: fix generic_fn_name generating incorrect names for C structs

[dy-tea]

Currently using C structs in generics does not work. Given the below files:

// foo.h
#ifndef TEST_H
#define TEST_H

struct foo {
  int a;
};

#endif

// generic_struct_cstruct_test.v
#insert "@VMODROOT/foo.h"

struct C.foo {
	a int
}

fn ref[T](x T) &T {
	return &x
}

fn test_main() {
	a := C.foo{}
	b := ref(a)
}

Currently outputs this C code:

VV_LOC struct foo* main__ref_T_struct foo(struct foo _v_toheap_x) {
struct foo* x = HEAP(struct foo, _v_toheap_x);
	return &(*(x));
}
VV_LOC void main__test_main(void) {
	struct foo a = ((struct foo){.a = 0,});
	struct foo* b = main__ref_T_struct foo(a);
}

Notice the space between main__ref_T_struct and foo on the first line.

This fails to compile:

/tmp/v_1000/generic_struct_cstruct_test.01K3EZ101KHRXGH9XKC03Q2DEW.tmp.c:1872:39: error: expected ‘=’, ‘,’, ‘;’, ‘asm’ or ‘__attribute__’ before ‘foo’
 1872 | VV_LOC struct foo* main__ref_T_struct foo(struct foo _v_toheap_x);
      |                                       ^~~
/tmp/v_1000/generic_struct_cstruct_test.01K3EZ101KHRXGH9XKC03Q2DEW.tmp.c:8195:39: error: expected ‘=’, ‘,’, ‘;’, ‘asm’ or ‘__attribute__’ before ‘foo’
 8195 | VV_LOC struct foo* main__ref_T_struct foo(struct foo _v_toheap_x) {
      |                                       ^~~
/tmp/v_1000/generic_struct_cstruct_test.01K3EZ101KHRXGH9XKC03Q2DEW.tmp.c: In function ‘main__test_main’:
/tmp/v_1000/generic_struct_cstruct_test.01K3EZ101KHRXGH9XKC03Q2DEW.tmp.c:8201:25: error: ‘main__ref_T_struct’ undeclared (first use in this function)
 8201 |         struct foo* b = main__ref_T_struct foo(a);
      |                         ^~~~~~~~~~~~~~~~~~
/tmp/v_1000/generic_struct_cstruct_test.01K3EZ101KHRXGH9XKC03Q2DEW.tmp.c:8201:25: note: each undeclared identifier is reported only once for each function it appears in
/tmp/v_1000/generic_struct_cstruct_test.01K3EZ101KHRXGH9XKC03Q2DEW.tmp.c:8201:44: error: expected ‘,’ or ‘;’ before ‘foo’
 8201 |         struct foo* b = main__ref_T_struct foo(a);
      |                                            ^~~

Wasn't sure if I should put the test under tests/generics or tests/c_structs. Let me know if I should change it.

[huly-for-github]

Connected to Huly®: V_0.6-24000

[spytheman]

Excellent work.