Add krelloptions variant that is used to turn on a configuration option to build the thread safe lightweight libraries.

var/spack/packages/mrnet/package.py

@@ -8,12 +8,17 @@ class Mrnet(Package):
     version('4.0.0', 'd00301c078cba57ef68613be32ceea2f')
     version('4.1.0', '5a248298b395b329e2371bf25366115c')
 
+    variant('krelloptions', default=False, description="Also build the MRNet LW threadsafe libraries")
     parallel = False
 
     depends_on("boost")
 
     def install(self, spec, prefix):
-        configure("--prefix=%s" %prefix, "--enable-shared")
+        # Build the MRNet LW thread safe libraries when the krelloptions variant is present
+        if '+krelloptions' in spec:
+           configure("--prefix=%s" %prefix, "--enable-shared", "--enable-ltwt-threadsafe")
+        else:
+           configure("--prefix=%s" %prefix, "--enable-shared")
 
         make()
         make("install")