[foreign-memaccess+abi] RFR: Minor Windows build fixes [v2]

[Jorn Vernee]

> Some minor changes to fix build errors/warnings on Windows:
> 
> - Remove spurious `vprintf`  declaration in libStdLibTest.h (it is already included as part of stdio.h). This was causing an error due to a conflicting declaration.
> - Remove `return` before free in benchmark lib. This was causing a warning that was then treated as an error.
> 
> Thanks,
> Jorn

Jorn Vernee has updated the pull request incrementally with one additional commit since the last revision:

  Remove libStdLibTest.h

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

Changes:
  - all: https://git.openjdk.java.net/panama-foreign/pull/528/files
  - new: https://git.openjdk.java.net/panama-foreign/pull/528/files/edca6059..49ea9ce0

Webrevs:
 - full: https://webrevs.openjdk.java.net/?repo=panama-foreign&pr=528&range=01
 - incr: https://webrevs.openjdk.java.net/?repo=panama-foreign&pr=528&range=00-01

  Stats: 54 lines in 2 files changed: 10 ins; 43 del; 1 mod
  Patch: https://git.openjdk.java.net/panama-foreign/pull/528.diff
  Fetch: git fetch https://git.openjdk.java.net/panama-foreign pull/528/head:pull/528

PR: https://git.openjdk.java.net/panama-foreign/pull/528