+ adding compiler features for no_std environments other than wasm (i.e. SGX) (#2421)

substrate/core/sr-std/Cargo.toml

@@ -13,3 +13,4 @@ default = ["std"]
 std = []
 nightly = []
 strict = []
+no_global_allocator = []

substrate/core/sr-std/without_std.rs

@@ -26,6 +26,7 @@ extern "C" {
 /// Wasm allocator
 pub struct WasmAllocator;
 
+#[cfg(not(feature = "no_global_allocator"))]
 #[global_allocator]
 static ALLOCATOR: WasmAllocator = WasmAllocator;