Update to llvm-ar's new argument format

llvm-ar bundled in the next llvm update will stop accepting the legacy
single-dash argument format.

Bug: 219872355
Test: presubmit
Change-Id: Iede68e4b13c3a01c176d26f335f96879c5c72c12
diff --git a/core/combo/select.mk b/core/combo/select.mk
index 7617558..9c7e69e 100644
--- a/core/combo/select.mk
+++ b/core/combo/select.mk
@@ -35,7 +35,7 @@
   ,HOST_CROSS builds are not supported in Make)
 else
 
-$(combo_var_prefix)GLOBAL_ARFLAGS := crsPD -format=gnu
+$(combo_var_prefix)GLOBAL_ARFLAGS := crsPD --format=gnu
 
 $(combo_var_prefix)STATIC_LIB_SUFFIX := .a