FIX(positional-audio): Force 8 bytes alignment for CCameraAngles in GTAV plugin

[davidebeatrici]

https://en.cppreference.com/w/cpp/language/alignas

This fixes compilation when the implicit alignment is not 8 bytes.

It can be the case with 32 bit targets.

---

Fixes #5849.

[davidebeatrici]

Turns out the #pragma is ignored in this specific case, you can test by passing -m32 to the compiler:

#include <cstdint>
#include <cstdio>

using ptr_t = uint64_t;

#pragma pack(push, 8)
struct CCameraAngles {
	uint8_t pad1[960];
	ptr_t playerAngles; // CPlayerAngles *
	uint8_t pad2[60];
};
#pragma pack(pop)

static_assert(sizeof(CCameraAngles) == 0x408, "");

int main() {
	printf("%zu\n", sizeof(CCameraAngles));

	return 0;
}

$ g++ -m32 test.cpp 
test.cpp:14:37: error: static assertion failed
   14 | static_assert(sizeof(CCameraAngles) == 0x408, "");
      |               ~~~~~~~~~~~~~~~~~~~~~~^~~~~~~~
test.cpp:14:37: note: the comparison reduces to ‘(1028 == 1032)’

The standard alignas specifier appears to work though, which is very nice as it looks better and #pragma stuff should be generally avoided.

Unfortunately there's a limitation, which would be why I didn't use it in the first place:

If the strictest (largest) alignas on a declaration is weaker than the alignment it would have without any alignas specifiers (that is, weaker than its natural alignment or weaker than alignas on another declaration of the same object or type), the program is ill-formed

plugins/gtav/structs.h:90:8: error: requested alignment is less than minimum alignment of 8 for type 'CPed'
struct alignas(4) CPed : public rage::fwEntity {
       ^
plugins/gtav/structs.h:215:1: error: static_assert failed due to requirement 'sizeof(CPed) == 5428' ""
static_assert(sizeof(CPed) == 0x1534, "");
^             ~~~~~~~~~~~~~~~~~~~~~~

Kind of disappointing.