rustc: Change wasm32-wasip2 to PIC-by-default

This commit changes the new `wasm32-wasip2` target to being PIC by
default rather than the previous non-PIC by default. This change is
intended to make it easier for the standard library to be used in a
shared object in its precompiled form. This comes with a hypothetical
modest slowdown but it's expected that this is quite minor in most use
cases or otherwise wasm compilers and/or optimizing runtimes can elide
the cost.

Author: alexcrichton

compiler/rustc_target/src/spec/targets/wasm32_wasip2.rs

@@ -18,7 +18,7 @@
 
 use crate::spec::crt_objects;
 use crate::spec::LinkSelfContainedDefault;
-use crate::spec::{base, Target};
+use crate::spec::{base, RelocModel, Target};
 
 pub fn target() -> Target {
     let mut options = base::wasm::options();
@@ -54,6 +54,11 @@ pub fn target() -> Target {
     // signatures.
     options.entry_name = "__main_void".into();
 
+    // Default to PIC unlike base wasm. This makes precompiled objects such as
+    // the standard library more suitable to be used with shared libaries a la
+    // emscripten's dynamic linking convention.
+    options.relocation_model = RelocModel::Pic;
+
     Target {
         llvm_target: "wasm32-wasip2".into(),
         metadata: crate::spec::TargetMetadata {