Bug 1414298: Don't try to set yasm version config settings if yasm isn't found. r=froydnj

MozReview-Commit-ID: LTDxJ5su7sM

--HG--
extra : rebase_source : ab80df38451c59760aad0931c66104480195fb96

build/moz.configure/toolchain.configure

@@ -57,12 +57,12 @@ def yasm_version(yasm):
     return Version(version)
 
 
-@depends(yasm_version)
+@depends_if(yasm_version)
 def yasm_major_version(yasm_version):
     return str(yasm_version.major)
 
 
-@depends(yasm_version)
+@depends_if(yasm_version)
 def yasm_minor_version(yasm_version):
     return str(yasm_version.minor)