build: abbreviate AR command, too

Summary:
The "ar" command was excessively verbose.
This abbreviates it to be like CC and LD.
Also, factor "rs" options into ARFLAGS.

Test Plan:
  $ rm librocksdb.a
  $ make librocksdb.a
  AR       librocksdb.a
  ar: creating librocksdb.a

Reviewers: ljin, sdong, igor.sugak, igor

Reviewed By: igor

Subscribers: dhruba

Differential Revision: https://reviews.facebook.net/D33699

.arcconfig

@@ -6,5 +6,10 @@
     "linters"
   ],
   "lint.engine" : "FacebookFbcodeLintEngine",
-  "lint.engine.single.linter" : "FbcodeCppLinter"
+  "lint.engine.single.linter" : "FbcodeCppLinter",
+  "base" : "git:HEAD^, hg:.^",
+  "git.default-relative-commit" : "HEAD^",
+  "git:arc.feature.start.default" : "origin/master",
+  "arc.feature.start.default" : "master",
+  "history.immutable" : false
 }

Makefile

@@ -10,6 +10,7 @@ CFLAGS += ${EXTRA_CFLAGS}
 CXXFLAGS += ${EXTRA_CXXFLAGS}
 LDFLAGS += $(EXTRA_LDFLAGS)
 MACHINE ?= $(shell uname -m)
+ARFLAGS = rs
 
 ifneq ($(MAKECMDGOALS),dbg)
 OPT += -O2 -fno-omit-frame-pointer
@@ -36,6 +37,10 @@ AM_V_GEN = $(am__v_GEN_$(V))
 am__v_GEN_ = $(am__v_GEN_$(AM_DEFAULT_VERBOSITY))
 am__v_GEN_0 = @echo "  GEN     " $@;
 am__v_GEN_1 =
+AM_V_at = $(am__v_at_$(V))
+am__v_at_ = $(am__v_at_$(AM_DEFAULT_VERBOSITY))
+am__v_at_0 = @
+am__v_at_1 =
 
 AM_V_CC = $(am__v_CC_$(V))
 am__v_CC_ = $(am__v_CC_$(AM_DEFAULT_VERBOSITY))
@@ -47,6 +52,10 @@ AM_V_CCLD = $(am__v_CCLD_$(V))
 am__v_CCLD_ = $(am__v_CCLD_$(AM_DEFAULT_VERBOSITY))
 am__v_CCLD_0 = @echo "  CCLD    " $@;
 am__v_CCLD_1 =
+AM_V_AR = $(am__v_AR_$(V))
+am__v_AR_ = $(am__v_AR_$(AM_DEFAULT_VERBOSITY))
+am__v_AR_0 = @echo "  AR      " $@;
+am__v_AR_1 =
 
 AM_LINK = $(AM_V_CCLD)$(CXX) $^ $(EXEC_LDFLAGS) -o $@ $(LDFLAGS) $(COVERAGEFLAGS)
 
@@ -356,8 +365,8 @@ package:
 # 	Unit tests and tools
 # ---------------------------------------------------------------------------
 $(LIBRARY): $(LIBOBJECTS)
-	rm -f $@
-	$(AR) -rs $@ $(LIBOBJECTS)
+	$(AM_V_AR)rm -f $@
+	$(AM_V_at)$(AR) $(ARFLAGS) $@ $(LIBOBJECTS)
 
 db_bench: db/db_bench.o $(LIBOBJECTS) $(TESTUTIL)
 	$(AM_LINK)