Another round of GCC fixes (#3115)

* Fix remaining <string> -> <cstring> for GCC compilation (#3114 follow-up)

MWerks' <string> header transitively includes C string functions
(memcpy, strlen, strcmp, etc.), but GCC/Clang's <string> is the C++
std::string header. These files all use C string functions and should
include <cstring> instead.

* Use std::isnan instead of isnan for GCC compilation

GCC's <cmath> places isnan in the std namespace. Using the unqualified
isnan fails to compile with GCC/Clang.

* Fix cCcD_Src types: s32 -> u32 for bitmask fields

cCcD_SrcObjCommonBase::mSPrm, cCcD_SrcObjTg::mType, and
cCcD_SrcObjAt::mType are used as bitmasks (SetType/SetSPrm take u32,
MskType/MskSPrm use u32, values like 0xFFFFFFFF are common in
aggregate inits). Change from s32 to u32 to match usage.

Also fix AT_TYPE_WOLF_ATTACK/AT_TYPE_UNK to use unsigned literals,
and remove now-unnecessary (s32) casts on hex literals in collision
source data.

* Mark dummy() functions as static to avoid multiple definition errors

These decomp artifact functions have the same name and signature across
TUs, causing linker errors when building as a single binary.

src/d/actor/d_a_e_hp.cpp

@@ -31,7 +31,7 @@ public:
 namespace {
 static dCcD_SrcCyl cc_hp_src = {
     {
-        {0, {{0x0, 0x0, 0x0}, {(s32)0xd8000000, 0x3}, 0x0}},
+        {0, {{0x0, 0x0, 0x0}, {0xd8000000, 0x3}, 0x0}},
         {dCcD_SE_13, 0, 0, 0, {0}},
         {dCcD_SE_NONE, 0, 0, 0, {6}},
         {0},
@@ -47,7 +47,7 @@ static dCcD_SrcCyl cc_hp_src = {
 
 static dCcD_SrcSph cc_lamp_src = {
     {
-        {0x0, {{0x0, 0x0, 0x0}, {(s32)0xD8FBFDFF, 0x43}, 0x75}},  // mObj
+        {0x0, {{0x0, 0x0, 0x0}, {0xD8FBFDFF, 0x43}, 0x75}},  // mObj
         {dCcD_SE_13, 0x0, 0x0, 0x0, 0x0},                         // mGObjAt
         {dCcD_SE_NONE, 0x0, 0x0, 0x0, 0x6},                       // mGObjTg
         {0x0},                                                    // mGObjCo