Make several functions static

* tests/argstr.c (argstr_suite): Make static.
* tests/basic.c (basic_suite): Likewise.
* tests/exec.c (exec_suite): Likewise.
* tests/inspect.c (inspect_suite): Likewise.
* tests/pump.c (pump_suite): Likewise.
* tests/read.c (read_suite): Likewise.
* tests/redirect.c (redirect_suite): Likewise.