nightly: use exact branch name in $BUILDVERSION_EXEC

Author: dancrossnyc

tools/helios-build/src/main.rs

@@ -599,7 +599,12 @@ fn regen_illumos_sh<P: AsRef<Path>>(
                 smatch,$SMATCHBIN,smatch\"\n";
         }
     }
-    env += "export BUILDVERSION_EXEC=\"git describe --all --long --dirty\"\n";
+    env += "helios_build_buildversion_exec_function() { \n\
+        git describe --all --long --dirty \
+        --match $(git branch --show-current) --exact-match 2>/dev/null || \
+        git describe --all --long --dirty \n\
+        }\n";
+    env += "export BUILDVERSION_EXEC=helios_build_buildversion_exec_function\n";
     env += &format!("export DMAKE_MAX_JOBS={}\n", maxjobs);
     env += "export ENABLE_SMB_PRINTING='#'\n";
     match relver {