RFR: 8264285: Clean the modification of ccstr JVM flags [v2]

[Ioi Lam]

> There are two versions of JVMFlagAccess::ccstrAtPut() for modifying JVM flags of the ccstr type (i.e., strings).
> 
> - One version requires the caller to free the old value, but some callers don't do that (writeableFlags.cpp).
> - The other version frees the old value on behalf of the caller. However, this version is accessible only via FLAG_SET_XXX macros and is currently unused. So it's unclear whether it actually works.
> 
> We should combine these two versions into a single function, fix problems in the callers, and add test cases. The old value should be freed automatically, because typically the caller isn't interested in the old value.
> 
> Note that the FLAG_SET_XXX macros do not return the old value. Requiring the caller of FLAG_SET_XXX to free the old value would be tedious and error prone.

Ioi Lam has updated the pull request incrementally with one additional commit since the last revision:

  relax flag attributions (ala JDK-7123237)

-------------

Changes:
  - all: https://git.openjdk.java.net/jdk/pull/3254/files
  - new: https://git.openjdk.java.net/jdk/pull/3254/files/7eca2343..673aaafc

Webrevs:
 - full: https://webrevs.openjdk.java.net/?repo=jdk&pr=3254&range=01
 - incr: https://webrevs.openjdk.java.net/?repo=jdk&pr=3254&range=00-01

  Stats: 37 lines in 4 files changed: 0 ins; 36 del; 1 mod
  Patch: https://git.openjdk.java.net/jdk/pull/3254.diff
  Fetch: git fetch https://git.openjdk.java.net/jdk pull/3254/head:pull/3254

PR: https://git.openjdk.java.net/jdk/pull/3254