profiler-builtins: define COMPILER_RT_HAS_UNAME on non-msvc platforms.

Otherwise lprofGetHostName, used by the PGO generator, won't be available.

This means that PGO and coverage profiling would be restricted to systems with
uname, but that seems acceptable.

Signed-off-by: Emilio Cobos Álvarez <emilio@crisal.io>

src/libprofiler_builtins/build.rs

@@ -50,6 +50,7 @@ fn main() {
         cfg.flag("-fomit-frame-pointer");
         cfg.flag("-ffreestanding");
         cfg.define("VISIBILITY_HIDDEN", None);
+        cfg.define("COMPILER_RT_HAS_UNAME", Some("1"));
     }
 
     for src in profile_sources {