RFR: 8224878: Use JVMFlag parameters instead of name strings

[Stefan Karlsson]

Hi all,

Please review this patch to use JVMFlag parameters instead of name 
strings in the JVM flag handling code.

https://bugs.openjdk.java.net/browse/JDK-8224878

The intention is to reduce the places where the API uses "const char* 
name" parameters to describe a JVM flag, and instead use a JVMFlag* when 
performing various flag handling code. The places where we translate 
from "const char* name" to JVMFlag* has been pushed to the outer layers 
of the code, which explicitly uses the JVMFlag::find_flag functions.

This allows us to replace strcmp with simple JVMFlag pointer equality 
checks in jvmFlagRangeList.cpp and jvmFlagConstraintList.cpp.

This gets rid of the need to store a typed pointer to the flag in 
jvmFlagRangeList.cpp and jvmFlagConstraintList.cpp.

This gets rid of the the need to propagate the 'allow_locked' and 
'return_flag' parameters down the call chain. For example, see the 
changes to JVMFlag::<type>At and JVMFlag::<type>AtPut:
-  static JVMFlag::Error intAt(const char* name, int* value, bool 
allow_locked = false, bool return_flag = false)      { return 
intAt(name, strlen(name), value, allow_locked, return_flag); }
+  static JVMFlag::Error intAt(const JVMFlag* flag, int* value);
   static JVMFlag::Error intAtPut(JVMFlag* flag, int* value, 
JVMFlag::Flags origin);
-  static JVMFlag::Error intAtPut(const char* name, size_t len, int* 
value, JVMFlag::Flags origin);
-  static JVMFlag::Error intAtPut(const char* name, int* value, 
JVMFlag::Flags origin)   { return intAtPut(name, strlen(name), value, 
origin); }

  It changes the JVMFlag::find_flag API. The way it uses default values 
have a surprising effect for users of those functions. find_flag(name) 
searches among all flags (even locked and constants), while 
find_flag(name, strlen(name)) doesn't return locked or constants flags. 
To make it less likely to accidentally call the wrong version, this has 
been changed to the following:
* JVMFlag::find_flag(name) - Fetches the flag if it is available 
(unlocked and not constant).
* JVMFlag::find_flag_unrestricted(name) - Fetches the flag even if it is 
locked or a constant.

Removed the unused JVMFlag::wasSetOnCmdline.

Small cleanups
- Renamed address_of_flag to flag_from_enum
- Renamed local JVMFlag* variable from results to flag
- Use initializer lists
- Removed superfluous semicolons

I don't mind splitting patch up into more than one RFE, if that seems 
more appropriate.

Tested with:
- test/hotspot/jtreg/runtime/CommandLine
- tier1 (tier2-3 80% done)

Suggestions on other testing is appreciated.

Thanks,
StefanK