Allow recipe to overide optimization.

fixes:

397 | #  warning _FORTIFY_SOURCE requires compiling with optimization (-O)
|       |    ^~~~~~~
| cc1: all warnings being treated as errors


Upstream-Status: OE specific

Signed-off-by: Armin Kuster <akuster808@gmail.com>

Index: src/makefile
===================================================================
--- src.orig/makefile
+++ src/makefile
@@ -43,7 +43,7 @@ CC = /usr/bin/gcc
 CCFLAGS = -Wall  			\
 	-Wmissing-declarations -Wmissing-prototypes -Wnested-externs \
 	-Werror -Wsign-compare \
-	 -c -ggdb -O0 			\
+	 -c -ggdb -O 			\
 	-DTPM_POSIX			\
 	-D_POSIX_			\
 	-DTPM_NUVOTON