linux-build: -std=gnu extensions + fix remaining snprintf decls

- CMakeLists: CMAKE_C_EXTENSIONS/CXX_EXTENSIONS ON. Strict -std=c11/c++20
  define __STRICT_ANSI__, which disables glibc _DEFAULT_SOURCE and hides
  clock_gettime(CLOCK_REALTIME) etc. that port/src/libultra.c needs.
  -std=gnu11/gnu++20 is GCC's default and what MinGW already used.
- port/src/{pccg,pcmodels,romdata}.c: local 'extern int snprintf(...,
  unsigned long long maxsize, ...)' decls conflict with glibc's size_t one
  (same bug already fixed in pc_protos.h in M-39); spell it size_t.
- libultra.c: drop the _GNU_SOURCE define (pulls cpu_set_t refs into
  <pthread.h> without <sched.h>); the D60 POSIX stack-bounds diagnostic
  now just prints n/a rather than needing pthread_getattr_np.

Windows: full rebuild 240/241, -level_09 crash-free past frame 1740.

CMakeLists.txt

@@ -52,9 +52,13 @@ include(TargetArch)
 include(FindPkgConfig)
 
 set(CMAKE_C_STANDARD 11)
-set(CMAKE_C_EXTENSIONS OFF)
+# GNU extensions ON: strict -std=c11/-std=c++20 define __STRICT_ANSI__, which
+# disables glibc's _DEFAULT_SOURCE and hides POSIX symbols the port needs
+# (clock_gettime/CLOCK_REALTIME in port/src/libultra.c, mmap flags, etc.).
+# -std=gnu11/gnu++20 is GCC's own default and what MinGW was already using.
+set(CMAKE_C_EXTENSIONS ON)
 set(CMAKE_CXX_STANDARD 20)
-set(CMAKE_CXX_EXTENSIONS OFF)
+set(CMAKE_CXX_EXTENSIONS ON)
 set(CMAKE_EXPORT_COMPILE_COMMANDS ON)
 
 # Default build type

port/src/libultra.c

@@ -1,8 +1,3 @@
-/* POSIX: enable clock_gettime(CLOCK_REALTIME/MONOTONIC) and pthread_getattr_np. */
-#if !defined(_WIN32) && !defined(_GNU_SOURCE)
-#define _GNU_SOURCE 1
-#endif
-
 /*
  * libultra OS shims for the PC port, plus the cooperative thread kernel.
  *
@@ -841,20 +836,10 @@ static void piServiceDma(s32 direction, u32 srcPA, void *dstVA, u32 size)
                               (uintptr_t)dstVA < (uintptr_t)thigh));
             }
 #else
-            {
-                pthread_attr_t at;
-                void *sbase = NULL;
-                size_t ssize = 0;
-                if (pthread_getattr_np(pthread_self(), &at) == 0) {
-                    pthread_attr_getstack(&at, &sbase, &ssize);
-                    pthread_attr_destroy(&at);
-                }
-                sysLogPrintf(LOG_ERROR,
-                             "D60 thread stack: %p..%p  dst-in-stack=%d\n",
-                             sbase, (void *)((uintptr_t)sbase + ssize),
-                             ((uintptr_t)dstVA >= (uintptr_t)sbase &&
-                              (uintptr_t)dstVA < (uintptr_t)sbase + ssize));
-            }
+            /* TEMP D60 diagnostic: no portable committed-stack query without
+             * _GNU_SOURCE (pthread_getattr_np); the raw stack window above and
+             * the crash handler's register dump are enough to symbolicate. */
+            sysLogPrintf(LOG_ERROR, "D60 thread stack: (n/a on POSIX)\n");
 #endif
             sysLogPrintf(LOG_ERROR,
                          "D60 BAD DMA TARGET dst=%p src=0x%08X size=0x%X "

port/src/pccg.c

@@ -22,7 +22,7 @@
 #include <string.h>
 
 extern void *malloc(unsigned long long size);
-extern int   snprintf(char *str, unsigned long long maxsize, const char *format, ...);
+extern int   snprintf(char *str, size_t maxsize, const char *format, ...);
 
 #include "platform.h"
 #include "system.h"

port/src/pcmodels.c

@@ -24,7 +24,7 @@
 /* D38: <stdlib.h>/<string.h> resolve to the decomp's N64 stubs via the
  * include path; declare the host functions this file uses. */
 extern void *malloc(unsigned long long size);
-extern int   snprintf(char *str, unsigned long long maxsize, const char *format, ...);
+extern int   snprintf(char *str, size_t maxsize, const char *format, ...);
 
 #include "platform.h"
 #include "system.h"

port/src/romdata.c

@@ -23,7 +23,7 @@
 /* D38: <stdio.h>/<stdlib.h> resolve to the decomp's N64 stubs via the include
  * path; declare the host functions this file uses. */
 extern void *malloc(unsigned long long size);
-extern int snprintf(char *str, unsigned long long maxsize, const char *format, ...);
+extern int snprintf(char *str, size_t maxsize, const char *format, ...);
 
 #include "platform.h"