Add a patch to fix gmp build using GCC 15

.github/workflows/build-ffmpeg.yml

@@ -54,7 +54,7 @@ jobs:
         run: |
           brew update
           brew unlink gettext libidn2 libpng libtiff libunistring libx11 libxau libxcb libxdmcp little-cms2 unbound
-      - uses: msys2/setup-msys2@c52d1fa9c7492275e60fe763540fb601f5f232a1
+      - uses: msys2/setup-msys2@v2
         if: matrix.os == 'windows-latest'
         with:
           install: base-devel mingw-w64-x86_64-gcc mingw-w64-x86_64-gperf mingw-w64-x86_64-nasm openssl-devel

patches/gmp.patch

@@ -0,0 +1,11 @@
+--- gmp-6.3.0/configure	2023-07-29 15:42:22.000000000 +0200
++++ gmp/configure	2025-02-03 22:00:33.567817886 +0100
+@@ -6568,7 +6566,7 @@
+
+ #if defined (__GNUC__) && ! defined (__cplusplus)
+ typedef unsigned long long t1;typedef t1*t2;
+-void g(){}
++void g(int a,t1 const*b,t1 c,t2 d,t1 const*e,int f){}
+ void h(){}
+ static __inline__ t1 e(t2 rp,t2 up,int n,t1 v0)
+ {t1 c,x,r;int i;if(v0){c=1;for(i=1;i<n;i++){x=up[i];r=x+1;rp[i]=r;}}return c;}

patches/winpthreads.patch

@@ -0,0 +1,26 @@
+Temporary patch for this issue:
+
+https://sourceforge.net/p/mingw-w64/mailman/message/59184409/
+
+This patch can be removed once msys2's packages have been updated.
+
+--- a/mingw-w64-libraries/winpthreads/include/pthread_time.h
++++ b/mingw-w64-libraries/winpthreads/include/pthread_time.h
+@@ -23,6 +23,7 @@
+ #ifndef WIN_PTHREADS_TIME_H
+ #define WIN_PTHREADS_TIME_H
+
++#include <sys/timeb.h>
+ #include "pthread_compat.h"
+
+ /* Posix timers are supported */
+--- a/mingw-w64-libraries/winpthreads/include/semaphore.h
++++ b/mingw-w64-libraries/winpthreads/include/semaphore.h
+@@ -23,6 +23,7 @@
+ #ifndef WIN_PTHREADS_SEMAPHORE_H
+ #define WIN_PTHREADS_SEMAPHORE_H
+
++#include <sys/timeb.h>
+ #include "pthread_compat.h"
+
+ #ifdef __cplusplus

scripts/build-ffmpeg.py

@@ -335,6 +335,10 @@ def main():
     builder = Builder(dest_dir=dest_dir)
     builder.create_directories()
 
+    # Fix winpthreads breakage until the fix reaches msys2 repos.
+    if plat == "Windows":
+        run(["patch", "-d", "C:/msys64/mingw64", "-i", os.path.join(builder.patch_dir, "winpthreads.patch"), "-p3"])
+
     # install packages
     available_tools = set()
     if plat == "Windows":