tell C compiler to put code and data in separate sections (pgcentralfoundation#2006)

Fixes a known issue (cshim requires LTO) in
pgcentralfoundation#1934.

Author: usamoi

.cargo/config.toml

@@ -7,6 +7,3 @@ r = "run --features"
 [target.'cfg(target_os="macos")']
 # Postgres symbols won't be available until runtime
 rustflags = ["-Clink-arg=-Wl,-undefined,dynamic_lookup"]
-
-[target.'cfg(target_env="msvc")']
-linker = "lld-link"

cargo-pgrx/src/templates/cargo_config_toml

@@ -1,6 +1,3 @@
 [target.'cfg(target_os="macos")']
 # Postgres symbols won't be available until runtime
 rustflags = ["-Clink-arg=-Wl,-undefined,dynamic_lookup"]
-
-[target.'cfg(target_env="msvc")']
-linker = "lld-link"

pgrx-bindgen/src/build.rs

@@ -1009,11 +1009,14 @@ fn build_shim(
     std::fs::copy(shim_src, shim_dst).unwrap();
 
     let mut build = cc::Build::new();
-    if let Some("msvc") = env_tracked("CARGO_CFG_TARGET_ENV").as_deref() {
-        // without this, pgrx_embed would be linked to postgres.lib
-        build.compiler("clang");
-        build.archiver("llvm-lib");
-        build.flag("-flto=thin");
+    let compiler = build.get_compiler();
+    if compiler.is_like_gnu() || compiler.is_like_clang() {
+        build.flag("-ffunction-sections");
+        build.flag("-fdata-sections");
+    }
+    if compiler.is_like_msvc() {
+        build.flag("/Gy");
+        build.flag("/Gw");
     }
     for pg_target_include in pg_target_includes(major_version, pg_config)?.iter() {
         build.flag(&format!("-I{pg_target_include}"));