Fix trivial no_std-breaking issues.

src/bssl.rs

@@ -22,7 +22,7 @@ use crate::{c, error};
 #[repr(transparent)]
 pub struct Result(c::int);
 
-impl From<Result> for ::std::result::Result<(), error::Unspecified> {
+impl From<Result> for core::result::Result<(), error::Unspecified> {
     fn from(ret: Result) -> Self {
         match ret.0 {
             1 => Ok(()),

src/error.rs

@@ -180,6 +180,7 @@ impl std::error::Error for KeyRejected {
     fn description(&self) -> &str { self.description_() }
 }
 
+#[cfg(feature = "use_heap")]
 impl std::fmt::Display for KeyRejected {
     fn fmt(&self, f: &mut core::fmt::Formatter) -> core::fmt::Result {
         f.write_str(self.description_())

src/lib.rs

@@ -113,6 +113,7 @@ mod rsa;
 
 pub mod signature;
 
+#[cfg(any(test, feature = "use_heap"))]
 pub mod test;
 
 mod sealed {

src/rand.rs

@@ -93,7 +93,10 @@ impl SecureRandom for SystemRandom {
 
 impl sealed::Sealed for SystemRandom {}
 
-#[cfg(not(any(target_os = "linux", target_os = "macos", target_os = "ios", windows)))]
+#[cfg(all(
+    feature = "use_heap",
+    not(any(target_os = "linux", target_os = "macos", target_os = "ios", windows))
+))]
 use self::urandom::fill as fill_impl;
 
 #[cfg(any(
@@ -182,6 +185,7 @@ mod sysrand {
 
 // Keep the `cfg` conditions in sync with the conditions in lib.rs.
 #[cfg(all(
+    feature = "use_heap",
     any(target_os = "redox", unix),
     not(any(target_os = "macos", target_os = "ios")),
     not(all(target_os = "linux", not(feature = "dev_urandom_fallback")))