Update GGML to b6646 (#12245)

Notable EOLs with this change:
- MacOS v12 and v13 are no longer supported (v14+ required)
- AMD gfx900 and gfx906 are no longer supported

llama/patches/0017-no-power-throttling-win32-with-gnuc.patch

@@ -8,10 +8,10 @@ Subject: [PATCH] no power throttling win32 with gnuc
  1 file changed, 1 insertion(+), 1 deletion(-)
 
 diff --git a/ggml/src/ggml-cpu/ggml-cpu.c b/ggml/src/ggml-cpu/ggml-cpu.c
-index a5689c18..85af19a3 100644
+index f8574d01..530efce0 100644
 --- a/ggml/src/ggml-cpu/ggml-cpu.c
 +++ b/ggml/src/ggml-cpu/ggml-cpu.c
-@@ -2412,7 +2412,7 @@ static bool ggml_thread_apply_priority(int32_t prio) {
+@@ -2431,7 +2431,7 @@ static bool ggml_thread_apply_priority(int32_t prio) {
          // Newer Windows 11 versions aggresively park (offline) CPU cores and often place
          // all our threads onto the first 4 cores which results in terrible performance with
          // n_threads > 4