feat: support build against system installed GGML library (#749)

Author: Seas0

CMakeLists.txt

@@ -33,6 +33,7 @@ option(SD_SYCL                       "sd: sycl backend" OFF)
 option(SD_MUSA                       "sd: musa backend" OFF)
 option(SD_FAST_SOFTMAX               "sd: x1.5 faster softmax, indeterministic (sometimes, same seed don't generate same image), cuda only" OFF)
 option(SD_BUILD_SHARED_LIBS          "sd: build shared libs" OFF)
+option(SD_USE_SYSTEM_GGML            "sd: use system-installed GGML library" OFF)
 #option(SD_BUILD_SERVER               "sd: build server example"                           ON)
 
 if(SD_CUDA)
@@ -124,7 +125,15 @@ add_definitions(-DGGML_MAX_NAME=128)
 # deps
 # Only add ggml if it hasn't been added yet
 if (NOT TARGET ggml)
-    add_subdirectory(ggml)
+    if (SD_USE_SYSTEM_GGML)
+        find_package(ggml REQUIRED)
+        if (NOT ggml_FOUND)
+            message(FATAL_ERROR "System-installed GGML library not found.")
+        endif()
+        add_library(ggml ALIAS ggml::ggml)
+    else()
+        add_subdirectory(ggml)
+    endif()
 endif()
 
 add_subdirectory(thirdparty)