bootstrap: Add directives to not double-link libs

Have all Cargo-built crates pass `--cfg cargobuild` and then add appropriate
`#[cfg]` definitions to all crates to avoid linking anything if this is passed.
This should help allow libstd to compile with both the makefiles and with Cargo.

1 files changed, 4 insertions, 1 deletions

diff --git a/src/libstd/rand/os.rs b/src/libstd/rand/os.rs
index 8d92909faf5..8a422246514 100644
--- a/src/libstd/rand/os.rs
+++ b/src/libstd/rand/os.rs
@@ -269,7 +269,10 @@ mod imp {
     const kSecRandomDefault: *const SecRandom = ptr::null();
 
     #[link(name = "Security", kind = "framework")]
-    extern "C" {
+    #[cfg(not(cargobuild))]
+    extern {}
+
+    extern {
         fn SecRandomCopyBytes(rnd: *const SecRandom,
                               count: size_t, bytes: *mut u8) -> c_int;
     }