RFR: 8289049: x86_32 build fails with GCC 11 due to newString646_US warning [v2]

[Aleksey Shipilev]

> See bug report for reproducer and error message. The warning looks quite superficial, and I initially suspected that it complains about `int len = (int)strlen(str)` cast of `size_t`. But what is confusing is nearly the similar code in `newStringCp1252`  apparently does not produce the warning: https://github.com/openjdk/jdk/blob/f5d1b5bda27c798347ae278cbf69725ed4be895c/src/java.base/share/native/libjava/jni_util.c#L533-L566
> 
> I propose we chalk it up to false/odd compiler warning and sync up unproblematic `newStringCp1252` and `newString646_US` implementation to dodge it.
> 
> Additional testing:
>  - [x] Linux x86_32 build with GCC 11
>  - [x]  Linux x86_32 `tier1` test with GCC 9
>  - [ ]  Linux x86_64 `tier1` test with GCC 9

Aleksey Shipilev has updated the pull request incrementally with one additional commit since the last revision:

  Init buf in newStringCp1252

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

Changes:
  - all: https://git.openjdk.org/jdk/pull/9702/files
  - new: https://git.openjdk.org/jdk/pull/9702/files/82ff99b3..adcbf91c

Webrevs:
 - full: https://webrevs.openjdk.org/?repo=jdk&pr=9702&range=01
 - incr: https://webrevs.openjdk.org/?repo=jdk&pr=9702&range=00-01

  Stats: 1 line in 1 file changed: 0 ins; 0 del; 1 mod
  Patch: https://git.openjdk.org/jdk/pull/9702.diff
  Fetch: git fetch https://git.openjdk.org/jdk pull/9702/head:pull/9702

PR: https://git.openjdk.org/jdk/pull/9702