Bug 1692909 - Follow-up: Fix building librnp on Windows. r=kaie

Add str-utils.cpp to files to build.

Differential Revision: https://phabricator.services.mozilla.com/D105340

--HG--
extra : amend_source : f8dc00cdb838324c21b69e4c21d2750bb2993bc3

third_party/rnp/moz.build

@@ -98,6 +98,7 @@ SYMBOLS_FILE = "rnp.symbols"
 SOURCES += [
     "src/common/file-utils.cpp",
     "src/common/list.cpp",
+    "src/common/str-utils.cpp",
     "src/lib/crypto.cpp",
     "src/lib/crypto/bn.cpp",
     "src/lib/crypto/dsa.cpp",