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/0016-add-C-API-for-mtmd_input_text.patch

@@ -10,7 +10,7 @@ Signed-off-by: Gabe Goodhart <ghart@us.ibm.com>
  2 files changed, 13 insertions(+)
 
 diff --git a/tools/mtmd/mtmd.cpp b/tools/mtmd/mtmd.cpp
-index a05373d5..6f70f7f4 100644
+index cd022c5e..3d680945 100644
 --- a/tools/mtmd/mtmd.cpp
 +++ b/tools/mtmd/mtmd.cpp
 @@ -79,6 +79,16 @@ enum mtmd_slice_tmpl {