build: enable PIC for static libghostty-vt

The static library was built without position-independent code,
which caused linker errors when consumers tried to link it into
PIE executables (the default on most Linux distributions). The
linker would fail with "relocation R_X86_64_32 against symbol
cannot be used when making a PIE object."

Enable PIC on the static library root module so it can be linked
into both PIE and non-PIE executables.

src/build/GhosttyLibVt.zig

@@ -100,6 +100,10 @@ fn initLib(
         // we'll cross that bridge when we get to it.
         lib.bundle_compiler_rt = true;
         lib.bundle_ubsan_rt = true;
+
+        // Enable PIC so the static library can be linked into PIE
+        // executables, which is the default on most Linux distributions.
+        lib.root_module.pic = true;
     }
 
     if (lib.rootModuleTarget().abi.isAndroid()) {