RFR: 8294549: configure script should detect unsupported path

[Mike Duigou]

The OpenJDK build system does not support building when the source code resides on a path that contains a space. This requirement is documented in the build instructions but not enforced by the configure script.

This change adds an explicit checks to the wrapper `configure` script that fail the build if the source code to be built is located in a directory who's path contains a space character or the build path cannot be determined.

Includes some idiom modernization and shell scripting best practices changes.

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Commit messages:
 - 8294549: configure script should detect unsupported path

Changes: https://git.openjdk.org/jdk/pull/10477/files
 Webrev: https://webrevs.openjdk.org/?repo=jdk&pr=10477&range=00
  Issue: https://bugs.openjdk.org/browse/JDK-8294549
  Stats: 24 lines in 1 file changed: 21 ins; 0 del; 3 mod
  Patch: https://git.openjdk.org/jdk/pull/10477.diff
  Fetch: git fetch https://git.openjdk.org/jdk pull/10477/head:pull/10477

PR: https://git.openjdk.org/jdk/pull/10477