r: add memory profiling variant (#8717)

* r: add memory profiling variant

* r: change memory_profiling to underscores

var/spack/repos/builtin/packages/r/package.py

@@ -62,6 +62,8 @@ class R(AutotoolsPackage):
             description='Links to externally installed BLAS/LAPACK')
     variant('X', default=False,
             description='Enable X11 support (call configure --with-x)')
+    variant('memory_profiling', default=False,
+            description='Enable memory profiling')
 
     # Virtual dependencies
     depends_on('blas', when='+external-lapack')
@@ -128,6 +130,9 @@ def configure_args(self):
         else:
             config_args.append('--without-x')
 
+        if '+memory_profiling' in spec:
+            config_args.append('--enable-memory-profiling')
+
         return config_args
 
     @run_after('install')