[Build Error] return type defaults to 'int'

[Zhihua Che]

Hi, everyone

        I'm building gdb using git repository and maybe find a bug.
After configure, several .c files are generated under <gdb-build>/gdb,
such as c-exp.c cp-name-parser.c, but they are all not complying with
c grammar. Precisely, the functions in them miss a return value, like
the below
        main() { return 0;}

        my code version is c338d4bceb084a629b479e1ac36ab2b42737e1c2.