Rollup merge of rust-lang#98149 - hoodmane:emscripten-pic, r=petrochenkov

Set relocation_model to Pic on emscripten target

So we can support dynamically linking libraries with Emscripten (otherwise we need to use nightly and `-Zbuild-std` to rebuild std with relocations).
```@sbc100```

Author: Dylan-DPC

compiler/rustc_target/src/spec/wasm32_unknown_emscripten.rs

@@ -1,5 +1,5 @@
 use super::{cvs, wasm_base};
-use super::{LinkArgs, LinkerFlavor, PanicStrategy, Target, TargetOptions};
+use super::{LinkArgs, LinkerFlavor, PanicStrategy, RelocModel, Target, TargetOptions};
 
 pub fn target() -> Target {
     let mut options = wasm_base::options();
@@ -26,6 +26,7 @@ pub fn target() -> Target {
         // functionality, and a .wasm file.
         exe_suffix: ".js".into(),
         linker: None,
+        relocation_model: RelocModel::Pic,
         panic_strategy: PanicStrategy::Unwind,
         no_default_libraries: false,
         post_link_args,