Add experimental raw-dylib feature to std

For Windows, this allows defining imports without needing the user to have import libraries. It's intended for this to become the default.

std/Cargo.toml

@@ -87,6 +87,10 @@ std_detect_file_io = ["std_detect/std_detect_file_io"]
 std_detect_dlsym_getauxval = ["std_detect/std_detect_dlsym_getauxval"]
 std_detect_env_override = ["std_detect/std_detect_env_override"]
 
+# Enable using raw-dylib for Windows imports.
+# This will eventually be the default.
+windows_raw_dylib = []
+
 [package.metadata.fortanix-sgx]
 # Maximum possible number of threads when testing
 threads = 125

std/src/sys/pal/windows/c/windows_targets.rs

@@ -3,6 +3,18 @@
 //! This is a simple wrapper around an `extern` block with a `#[link]` attribute.
 //! It's very roughly equivalent to the windows-targets crate.
 
+#[cfg(feature = "windows_raw_dylib")]
+pub macro link {
+    ($library:literal $abi:literal $($link_name:literal)? $(#[$doc:meta])? fn $($function:tt)*) => (
+        #[cfg_attr(not(target_arch = "x86"), link(name = $library, kind = "raw-dylib", modifiers = "+verbatim"))]
+        #[cfg_attr(target_arch = "x86", link(name = $library, kind = "raw-dylib", modifiers = "+verbatim", import_name_type = "undecorated"))]
+        extern $abi {
+            $(#[link_name=$link_name])?
+            pub fn $($function)*;
+        }
+    )
+}
+#[cfg(not(feature = "windows_raw_dylib"))]
 pub macro link {
     ($library:literal $abi:literal $($link_name:literal)? $(#[$doc:meta])? fn $($function:tt)*) => (
         // Note: the windows-targets crate uses a pre-built Windows.lib import library which we don't
@@ -17,6 +29,7 @@ pub macro link {
     )
 }
 
+#[cfg(not(feature = "windows_raw_dylib"))]
 #[link(name = "advapi32")]
 #[link(name = "ntdll")]
 #[link(name = "userenv")]

sysroot/Cargo.toml

@@ -27,3 +27,4 @@ profiler = ["std/profiler"]
 std_detect_file_io = ["std/std_detect_file_io"]
 std_detect_dlsym_getauxval = ["std/std_detect_dlsym_getauxval"]
 std_detect_env_override = ["std/std_detect_env_override"]
+windows_raw_dylib = ["std/windows_raw_dylib"]