[BOLT][NFC] Clarify requirement of PLTCall pass

PLTCall does not depend on linking the input with -znow: it sets the
DF_BIND_NOW and/or DF_1_NOW tags for the output binary.
The requirement is that the input contains either FLAGS or FLAGS_1
dynamic entries.

Author: bgergely0

bolt/lib/Passes/PLTCall.cpp

@@ -23,7 +23,7 @@ namespace opts {
 extern cl::OptionCategory BoltOptCategory;
 
 static cl::opt<bolt::PLTCall::OptType>
-    PLT("plt", cl::desc("optimize PLT calls (requires linking with -znow)"),
+    PLT("plt", cl::desc("optimize PLT calls (sets DF_BIND_NOW/DF_1_NOW in the output binary)"),
         cl::init(bolt::PLTCall::OT_NONE),
         cl::values(clEnumValN(bolt::PLTCall::OT_NONE, "none",
                               "do not optimize PLT calls"),