[jdk11u-dev] RFR: 8299616: [11u] Bootcycle build fails after JDK-8257679 backport

[Aleksey Shipilev]

Currently, JDK 11u `make bootcycle-images` fails with:


 bootcycle-spec.gmk:32: *** non-numeric first argument to `word' function: ''. Stop.


The apparent reason is [JDK-8257679](https://bugs.openjdk.org/browse/JDK-8257679) that did the following change:
 https://github.com/openjdk/jdk11u-dev/commit/40f4fc2da8532252a1660c7f082eb19046f4bc70#diff-935527b393cb4625a8874febf5fe39d43479a2228ef437f4e104ba3001e1e30fL31-L40

Note that the left-over hunk uses `JAVA_EXEC_POS`, which is defined in the hunk that was removed. This PR reinstantiates that hunk.

Additional testing:
 - [x] Linux x86_64 fastdebug `make bootcycle-images`
 - [ ] Windows x86_64 fastdebug `make bootcycle-images`

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

Commit messages:
 - Fix

Changes: https://git.openjdk.org/jdk11u-dev/pull/1639/files
 Webrev: https://webrevs.openjdk.org/?repo=jdk11u-dev&pr=1639&range=00
  Issue: https://bugs.openjdk.org/browse/JDK-8299616
  Stats: 8 lines in 1 file changed: 8 ins; 0 del; 0 mod
  Patch: https://git.openjdk.org/jdk11u-dev/pull/1639.diff
  Fetch: git fetch https://git.openjdk.org/jdk11u-dev pull/1639/head:pull/1639

PR: https://git.openjdk.org/jdk11u-dev/pull/1639