RFR: 8257905: Make fixpath.sh more liberal in accepting paths embedded in arguments [v2]

[Magnus Ihse Bursie]

> When calling a Windows tool that needs an argument on the form `-option/a:/home/ihse/myjdk/...`, fixpath gets confused and thinks `/a:/home/ihse/myjdk` is a unix path, notices that it does not exists, and stops trying to convert the path. 
> 
> Instead it needs to recheck for paths after a separator such as `:` or `=`.

Magnus Ihse Bursie has updated the pull request incrementally with one additional commit since the last revision:

  The same fix is also needed for the $DRIVEPREFIX regex

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Changes:
  - all: https://git.openjdk.java.net/jdk/pull/1698/files
  - new: https://git.openjdk.java.net/jdk/pull/1698/files/ae993372..b678804e

Webrevs:
 - full: https://webrevs.openjdk.java.net/?repo=jdk&pr=1698&range=01
 - incr: https://webrevs.openjdk.java.net/?repo=jdk&pr=1698&range=00-01

  Stats: 1 line in 1 file changed: 0 ins; 0 del; 1 mod
  Patch: https://git.openjdk.java.net/jdk/pull/1698.diff
  Fetch: git fetch https://git.openjdk.java.net/jdk pull/1698/head:pull/1698

PR: https://git.openjdk.java.net/jdk/pull/1698