[jdk11u-dev] RFR: 8357657: [11u][windows] cannot stat '/jdk.crypto.ec/*': No such file or directory

[Sergey Bylokhov]

This patch provides a workaround for a bug in the latest version of Cygwin. Only JDK 11 is affected; newer versions are not impacted because the makefiles were updated by [JDK-8220383](https://bugs.openjdk.org/browse/JDK-8220383).

The issue is that:
`ifneq ($(wildcard $(IMPORT_MODULES_CLASSES)/$(MODULE)), )`
returns results even when `IMPORT_MODULES_CLASSES` is empty/unset. This causes the build to incorrectly search for a module like `/jdk.crypto.ec/`, which fails because the directory does not exist.

The fix is to first check whether `IMPORT_MODULES_CLASSES` is set. If it is, we define `IMPORT_MODULE_DIR` as `$(IMPORT_MODULES_CLASSES)/$(MODULE)` and use this property consistently throughout the build. This matches the approach introduced in [JDK-8220383](https://cr.openjdk.org/~erikj/8220383/webrev.01/make/CompileJavaModules.gmk.sdiff.html) for this codepath.

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Commit messages:
 - Merge branch 'openjdk:master' into JDK-8357657
 - 8357657: [11u][windows] cannot stat '/jdk.crypto.ec/*': No such file or directory

Changes: https://git.openjdk.org/jdk11u-dev/pull/3035/files
  Webrev: https://webrevs.openjdk.org/?repo=jdk11u-dev&pr=3035&range=00
  Issue: https://bugs.openjdk.org/browse/JDK-8357657
  Stats: 10 lines in 1 file changed: 5 ins; 0 del; 5 mod
  Patch: https://git.openjdk.org/jdk11u-dev/pull/3035.diff
  Fetch: git fetch https://git.openjdk.org/jdk11u-dev.git pull/3035/head:pull/3035

PR: https://git.openjdk.org/jdk11u-dev/pull/3035