RFR: 8343452: Incorrect WINDOWS build variable is used in macroAssembler_x86.cpp

[theoweidmannoracle]

>From JBS:

> HotSpot VM build macro defines _WINDOWS env variable only.
> call_clobbered_gp_registers() and call_clobbered_xmm_registers() incorrectly use WINDOWS (without underscore).
> RSI and RDI are missing from list of clobbered register on windows due to that and may cause issue when calling native code which modifies them.
> 
> AMM register are less affected because all XMM registers are listed as clobbered.
> 
> The code was added by [JDK-8283327](https://bugs.openjdk.org/browse/JDK-8283327) changes in JDK 19.

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Commit messages:
 - Fix macro name

Changes: https://git.openjdk.org/jdk/pull/21901/files
  Webrev: https://webrevs.openjdk.org/?repo=jdk&pr=21901&range=00
  Issue: https://bugs.openjdk.org/browse/JDK-8343452
  Stats: 2 lines in 1 file changed: 0 ins; 0 del; 2 mod
  Patch: https://git.openjdk.org/jdk/pull/21901.diff
  Fetch: git fetch https://git.openjdk.org/jdk.git pull/21901/head:pull/21901

PR: https://git.openjdk.org/jdk/pull/21901