build: allow specifying custom linker flags

This is useful for people who want to link using recent versions of
mold which are smart enough to e.g. optimise GOT loads; we need to
pass --no-relax to disable those optimisations in order to get matching
instructions.

toolchain/ToolchainNX64.cmake

@@ -41,6 +41,9 @@ add_link_options(-fPIC -Wl,-Bsymbolic-functions -shared)
 if (DEFINED UKING_LINKER)
     message(STATUS "Using custom linker: ${UKING_LINKER}")
     add_link_options(-fuse-ld=${UKING_LINKER})
+    if (DEFINED UKING_LINKER_FLAGS)
+        add_link_options(${UKING_LINKER_FLAGS})
+    endif()
 else()
     # Use lld for performance reasons (and because we don't want a dependency on GNU tools)
     add_link_options(-fuse-ld=lld)