zig build: linkSystemLibrary integrates with pkg-config

* add -D CLI option for setting C macros
 * add std.ascii.allocLowerString
 * add std.ascii.eqlIgnoreCase
 * add std.ascii.indexOfIgnoreCasePos
 * add std.ascii.indexOfIgnoreCase
29b82d20a4Andrew Kelley committed on 9/23/2019, 6:45:14 PMparent35c1d8c
3 files changedLine totals unavailable