Keep symbols even for production release.

Summary:
Keeping symbols in the binary increases the size of the library but makes
it easier to debug. The optimization level is still -O2, so this should
have no impact on performance.

Test Plan: make all

Reviewers: heyongqiang, MarkCallaghan

Reviewed By: MarkCallaghan

CC: MarkCallaghan

Differential Revision: https://reviews.facebook.net/D5601

Makefile

@@ -9,9 +9,9 @@ INSTALL_PATH ?= $(CURDIR)
 # Uncomment exactly one of the lines labelled (A), (B), and (C) below
 # to switch between compilation modes.
 
-OPT ?= -O2 -DNDEBUG       # (A) Production use (optimized mode)
+# OPT ?= -O2 -DNDEBUG       # (A) Production use (optimized mode)
 # OPT ?= -g2              # (B) Debug mode, w/ full line-level debugging symbols
-# OPT ?= -O2 -g2 -DNDEBUG # (C) Profiling mode: opt, but w/debugging symbols
+OPT ?= -O2 -g2 -DNDEBUG # (C) Profiling mode: opt, but w/debugging symbols
 #-----------------------------------------------
 
 # detect what platform we're building on