Bug 1349002 - Build DMD with unified sources. r=njn

DMD can be built with unified sources, additionally it doesn't need NSPR's
strcpy to build properly.

MozReview-Commit-ID: 9hZFlpWdt7

memory/replace/dmd/moz.build

@@ -8,7 +8,7 @@ EXPORTS += [
     'DMD.h',
 ]
 
-SOURCES += [
+UNIFIED_SOURCES += [
     '../../../mfbt/HashFunctions.cpp',
     '../../../mfbt/JSONWriter.cpp',
     '../../../mfbt/Poison.cpp',
@@ -16,10 +16,6 @@ SOURCES += [
     'DMD.cpp',
 ]
 
-SOURCES += [
-    '../../../nsprpub/lib/libc/src/strcpy.c',
-]
-
 SharedLibrary('dmd')
 
 DEFINES['MOZ_NO_MOZALLOC'] = True