BUILD | SHIELD_PACK | HADGEN problem including stdlib.h

When building latest dev with GCC 11.2.1 a warning is produced for files shield_pack/hadgen/inc/hadgen_time.c and shield_pack/hadgen/src/hadgen_options.c stating implicit declaration of function (abs|srand|rand). This can be fixed, adding missing header stdlib.h as is adviced by the compiler, but afterwards error appears stating that there is error in shield_pack/hadgen/inc/hadgen_common_blocks.h random redeclared as different kind of symbol. Apparently stdlib.h adds something, that hadgen_common_blocks.h does not like.