unix/Makefile: Disable assertions in the standard unix executable.

Reasons to disable:
- the code is relatively robust so doesn't need full checking in the
  main executable, and the coverage build is used for full testing
  with assertions still enabled;
- reduces code size noticeably, by 27k for x86-64 and 20k for x86;
- allows to more easily track changes in code size, since assertions
  can skew things.

unix/Makefile

@@ -30,7 +30,7 @@ ifdef DEBUG
 CFLAGS += -g
 COPT = -O0
 else
-COPT = -Os -fdata-sections -ffunction-sections #-DNDEBUG
+COPT = -Os -fdata-sections -ffunction-sections -DNDEBUG
 # _FORTIFY_SOURCE is a feature in gcc/glibc which is intended to provide extra
 # security for detecting buffer overflows. Some distros (Ubuntu at the very least)
 # have it enabled by default.