Pass the mcmodel=medium parameter to CC via GHC

Ensure that GHC-driver builds default to mcmodel=medium, so that GHC
passes this default parameter to CC without having to add it to the
compiled project.

Commit e70d4140 does not ensure that all
GHC-built object files have a default model of medium, and will raise an
R_LARCH_B26 overflow error.

m4/fptools_set_c_ld_flags.m4

@@ -105,6 +105,10 @@ AC_DEFUN([FPTOOLS_SET_C_LD_FLAGS],
         $5="$$5 -D_THREAD_SAFE"
         ;;
 
+    loongarch64*linux*)
+        $2="$$2 -mcmodel=medium"
+        ;;
+
     esac
 
     AC_MSG_RESULT([done])