linux-runtime: declare getenv()/realloc() for the strict-host build

The N64 <stdlib.h> stub declares neither. MinGW's other CRT headers leak
them; a strict host GCC (Linux/macOS, -std=gnu11) does not, so getenv()'s
64-bit char* return is assumed int and truncated -> configGetFrameDump
(GE_PCDUMP path) dereferenced a low-32 pointer and segfaulted. Add K&R
decls: pc_protos.h (D38 mechanism -> game TUs via <ultra64.h>) and the
port/shim/stdlib.h non-Windows branch (-> port TUs that #include
<stdlib.h>). K&R form stays compatible with the real prototypes; malloc/
calloc/free are already covered elsewhere so not repeated.

port/include/pc_protos.h

@@ -201,6 +201,11 @@ void fileUpdateSelectedBondInSave();
 s32 fogGetPropDistColor();
 void fogLoadLevelEnvironment();
 void free();
+/* D38: the N64 <stdlib.h> stub declares neither, and unlike MinGW a strict
+ * host GCC does not leak them — so getenv()'s 64-bit pointer return is
+ * truncated to int (crashed configGetFrameDump on Linux). */
+char * getenv();
+void * realloc();
 int frontGetPlayersFavoriteWeaponInHand();
 void generate_player_thrown_grenade();
 void generate_player_thrown_knife();

port/shim/stdlib.h

@@ -17,4 +17,15 @@
 #include "hoststdlib.h"
 #else
 #include "include/stdlib.h"
+#if !defined(_WIN32)
+/* The N64 stub declares only lldiv_t/ldiv_t + lldiv/ldiv. MinGW's other CRT
+ * headers leak getenv() etc.; a strict host GCC (Linux/macOS) does not, so
+ * getenv()'s 64-bit pointer return is assumed int and truncated (crashed
+ * configGetFrameDump). Declare the pointer-returning stragglers the port +
+ * game code use that nothing else declares. K&R form = compatible with any
+ * real prototype. (malloc/calloc/free are in port/include/pc_protos.h and
+ * a few port TUs' own local decls — not repeated here to avoid conflicts.) */
+extern char *getenv();
+extern void *realloc();
+#endif
 #endif