build: make the Zig static lib position-independent (PIC)

The static lib's code had absolute relocations (R_X86_64_32S against
character_map), so linking it into a PIE executable failed on Linux
('can not be used when making a PIE object') — which broke test-ffi-cli on
Garnix and would break any Linux FFI consumer building a default PIE binary.
Set .pic = true on the static-lib module. (Masked on darwin by its reloc model.)

Author: pmarreck

build.zig

@@ -21,6 +21,9 @@ pub fn build(b: *std.Build) void {
         .root_source_file = b.path("src/zig/printable_binary.zig"),
         .target = target,
         .optimize = optimize,
+        // Position-independent so the static lib links into PIE executables
+        // (the default on modern Linux) — required by FFI consumers.
+        .pic = true,
     });
     static_lib_mod.addAnonymousImport("character_map.txt", .{ .root_source_file = b.path("character_map.txt") });