Remove -O0 change

Author: ThomasHickman

Makefile

@@ -33,7 +33,7 @@ CPPFLAGS =
 # TODO: probably update cram code to make it compile cleanly with -Wc++-compat
 # For testing strict C99 support add -std=c99 -D_XOPEN_SOURCE=600
 #CFLAGS   = -g -Wall -O2 -pedantic -std=c99 -D_XOPEN_SOURCE=600 -D__FUNCTION__=__func__
-CFLAGS   = -g -Wall -O0
+CFLAGS   = -g -Wall -O2
 EXTRA_CFLAGS_PIC = -fpic
 LDFLAGS  =
 LIBS     = $(htslib_default_libs)