[build] Enable strip for libtaichi_c_api.so with Release Build (#6845)

Issue: #6793

  | Size (Original) | Size (Optimized)
-- | -- | --
Vulkan | 14 MB | 1.5 MB
Vulkan + LLVM | 82 MB | 51 MB

libtaichi_c_api.so built with LLVM does not benefit much from function
level linking, mainly because libLLVM.a is not compiled with
`-ffunction-sections -fdata-sections`. We'll have that fixed later.

cmake/TaichiCAPI.cmake

@@ -20,7 +20,6 @@ endif()
 endfunction()
 
 set(TAICHI_C_API_NAME taichi_c_api)
-
 file(GLOB_RECURSE C_API_SOURCE "c_api/src/taichi_core_impl.cpp")
 
 if (TI_WITH_LLVM)
@@ -50,6 +49,9 @@ add_library(${TAICHI_C_API_NAME} SHARED ${C_API_SOURCE})
 target_link_static_library(${TAICHI_C_API_NAME} taichi_core)
 target_enable_function_level_linking(${TAICHI_C_API_NAME})
 
+# Strip shared library
+set_target_properties(${TAICHI_C_API_NAME} PROPERTIES LINK_FLAGS_RELEASE -s)
+
 # Avoid exporting third party symbols from libtaichi_c_api.so
 # Note that on Windows, external symbols will be excluded from .dll automatically, by default.
 if(LINUX)