-frandom-seed=string
 This option provides a seed that GCC uses when it would otherwise
 use random numbers. It is used to generate certain symbol names
 that have to be different in every compiled file.  It is also used
 to place unique stamps in coverage data files and the object files
 that produce them. You can use the -frandom-seed option to produce
 reproducibly identical object files.

 The string should be different for every file you compile.