RFR: 8258925: configure script failed on WSL

[Yasumasa Suenaga]

I ran configure script on WSL 1, but it failed as below:

$ bash configure --enable-debug --with-boot-jdk=/mnt/d/Java/jdk-15.0.1

    :

configure: Found potential Boot JDK using configure arguments
configure: The command for java_to_test, which resolves as "/mnt/d/Java/jdk-15.0.1/bin/java", can not be found.
configure: error: Cannot locate /mnt/d/Java/jdk-15.0.1/bin/java
configure exiting with result code 1

`fixpath.sh` attempts to run `$PATHTOOL` with `.exe` if it fails with original path, but `.exe` would not be added even if `$path.exe` exists.

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

Commit messages:
 - 8258925: configure script failed on WSL

Changes: https://git.openjdk.java.net/jdk/pull/1889/files
 Webrev: https://webrevs.openjdk.java.net/?repo=jdk&pr=1889&range=00
  Issue: https://bugs.openjdk.java.net/browse/JDK-8258925
  Stats: 2 lines in 1 file changed: 1 ins; 0 del; 1 mod
  Patch: https://git.openjdk.java.net/jdk/pull/1889.diff
  Fetch: git fetch https://git.openjdk.java.net/jdk pull/1889/head:pull/1889

PR: https://git.openjdk.java.net/jdk/pull/1889