libcap: Fix compile warnings.

The tautological comparison happens as part of a validity check and
should be harmless.

Also, make it always compile with Clang.

Bug: None
Change-Id: I8b02552f9f9ca0148e2795a25cc240316528e11e
diff --git a/Android.mk b/Android.mk
index 02af05c..0fd42fc 100644
--- a/Android.mk
+++ b/Android.mk
@@ -23,8 +23,12 @@
     libcap/cap_text.c
 
 
+libcap_cflags := -Wno-unused-parameter -Wno-tautological-compare
+
 # Shared library.
 include $(CLEAR_VARS)
+LOCAL_CLANG := true
+LOCAL_CFLAGS := $(libcap_cflags)
 LOCAL_SRC_FILES := $(libcap_src_files)
 
 LOCAL_C_INCLUDES += $(LOCAL_PATH)/libcap/include
@@ -36,6 +40,8 @@
 
 # Static library.
 include $(CLEAR_VARS)
+LOCAL_CLANG := true
+LOCAL_CFLAGS := $(libcap_cflags)
 LOCAL_SRC_FILES := $(libcap_src_files)
 
 LOCAL_C_INCLUDES += $(LOCAL_PATH)/libcap/include