code checking: fix compile errors and warnings

code checking: fix compile errors and warnings

The following compile error and warning messages have been fixed:

gcc -c -I. -Iproto -DHAVE_CONFIG_H     -g -O2 -D_FORTIFY_SOURCE=1
   -o objects/code_check.o code_check.c
code_check.c: In function 'cc_slave_sroutine':
code_check.c:315: error: 'gui' undeclared (first use in this function)
code_check.c:315: error: (Each undeclared identifier is reported only once
code_check.c:315: error: for each function it appears in.)
code_check.c: In function 'cc_update_screen':
code_check.c:364: error: 'gui' undeclared (first use in this function)
code_check.c: In function 'cc_compile_tmp_copy':
code_check.c:500: warning: ignoring return value of 'system', declared
with attribute warn_unused_result
code_check.c: In function 'cc_create_tmp_copy':
code_check.c:520: warning: ignoring return value of 'system', declared
with attribute warn_unused_result
make[1]: *** [objects/code_check.o] Error 1