Don't define posix macros that we don't support

[sbc100]

While -1 is valid value for these, simply not defining them is perfectly acceptable and has the same meaning AFAICT. This makes the patch smaller, and also works for codebased that use #ifdef

This change was original made in #9452.

[sbc100]

From https://pubs.opengroup.org/onlinepubs/000095399/ docs on unistd.h:

Constants for Options and Option Groups
The following symbolic constants, if defined in <unistd.h>, shall have a value of -1, 0, or greater, unless otherwise specified below. If these are undefined, the fpathconf(), pathconf(), or sysconf() functions can be used to determine whether the option is provided for a particular invocation of the application.

If a symbolic constant is defined with the value -1, the option is not supported. Headers, data types, and function interfaces required only for the option need not be supplied. An application that attempts to use anything associated only with the option is considered to be requiring an extension.

If a symbolic constant is defined with a value greater than zero, the option shall always be supported when the application is executed. All headers, data types, and functions shall be present and shall operate as specified.

If a symbolic constant is defined with the value zero, all headers, data types, and functions shall be present. The application can check at runtime to see whether the option is supported by calling fpathconf(), pathconf(), or sysconf() with the indicated name parameter.

Unless explicitly specified otherwise, the behavior of functions associated with an unsupported option is unspecified, and an application that uses such functions without first checking fpathconf(), pathconf(), or sysconf() is considered to be requiring an extension.

For conformance requirements, refer to Conformance.

[sbc100]

Not worth it actually..