Some GCC compilation fixes (#3114)

* Fix 6-byte multichar literals

* Add `struct` to `e_ga_class::ga_s`

* Fix remaining wrong forward declares (struct/class)

* Replace `#include <string>` with `#include <cstring>`

* Guard FLT_EPSILON define to prevent redefinition

* Add missing `#include <cstring>` for direct cstring function usage

include/d/actor/d_a_e_ga.h

@@ -34,7 +34,7 @@ public:
     /* 0x0570 */ u8 prm0;
     /* 0x0571 */ u8 prm1;
     /* 0x0572 */ u8 prm2;
-    /* 0x0574 */ ga_s ga_s[256];
+    /* 0x0574 */ struct ga_s ga_s[256];
     /* 0x4D74 */ int ga_num;
     /* 0x4D78 */ u8 HIOInit;
     /* 0x4D79 */ u8 initialized;

include/d/actor/d_a_e_pm.h

@@ -9,7 +9,7 @@
 #include "d/d_cc_uty.h"
 #include "d/d_msg_flow.h"
 
-class dPath;
+struct dPath;
 
 /**
  * @ingroup actors-enemies

include/d/actor/d_a_npc.h

@@ -10,6 +10,7 @@
 #include "d/d_msg_flow.h"
 #include "d/d_particle_copoly.h"
 #include "global.h"
+#include <cstring>
 
 struct daNpc_GetParam1 {  // name unknown
     /* 0x0 */ int fileIdx;

include/d/actor/d_a_npc_bou.h

@@ -2,6 +2,7 @@
 #define D_A_NPC_BOU_H
 
 #include "d/actor/d_a_npc.h"
+#include <cstring>
 
 struct daNpc_Bou_HIOParam {
     /* 0x00 */ daNpcT_HIOParam common;

include/d/actor/d_a_npc_cdn3.h

@@ -4,6 +4,7 @@
 #include "d/actor/d_a_npc.h"
 #include "d/actor/d_a_npc_cd2.h"
 #include "d/actor/d_a_tag_schedule.h"
+#include <cstring>
 
 /**
  * @ingroup actors-npcs

include/d/actor/d_a_npc_kn.h

@@ -2,6 +2,7 @@
 #define D_A_NPC_KN_H
 
 #include "d/actor/d_a_npc.h"
+#include <cstring>
 
 struct daNpc_Kn_HIOParam {
     /* 0x00 */ daNpcT_HIOParam common;

include/d/actor/d_a_npc_kolin.h

@@ -2,6 +2,7 @@
 #define D_A_NPC_KOLIN_H
 
 #include "d/actor/d_a_npc.h"
+#include <cstring>
 
 struct daNpc_Kolin_HIOParam {
     /* 0x00 */ daNpcT_HIOParam common;

include/d/actor/d_a_npc_the.h

@@ -2,6 +2,7 @@
 #define D_A_NPC_THE_H
 
 #include "d/actor/d_a_npc4.h"
+#include <cstring>
 
 struct daNpcThe_HIOParam {
     /* 0x00 */ daNpcF_HIOParam common;

include/d/actor/d_a_obj_cblock.h

@@ -5,7 +5,7 @@
 #include "d/d_cc_d.h"
 #include "f_op/f_op_actor_mng.h"
 
-class dPath;
+struct dPath;
 
 /**
  * @ingroup actors-objects

include/d/actor/d_a_passer_mng.h

@@ -5,7 +5,7 @@
 #include "d/d_kankyo.h"
 #include "f_op/f_op_actor_mng.h"
 
-class dPath;
+struct dPath;
 
 /**
  * @ingroup actors-unsorted