use single slash version of -print-whatever

The double slash variants are not documented in GCC manual.  Therefore,
it is better to use the single slash variants as usual.
diff --git a/core/combo/ b/core/combo/
index 8c89143..c3ea816 100644
--- a/core/combo/
+++ b/core/combo/
@@ -177,7 +177,7 @@
 target_libgcov := $(shell $(TARGET_CC) $(TARGET_GLOBAL_CFLAGS) \
-        --print-file-name=libgcov.a)
+        -print-file-name=libgcov.a)
 ifneq ($(strip $(BUILD_FDO_INSTRUMENT)),)
   # Set BUILD_FDO_INSTRUMENT=true to turn on FDO instrumentation.
   # The profile will be generated on /data/local/tmp/profile on the device.