RFR: 8211362: Restrict export of libjpeg symbols from libjavafx_iio.so

[Johan Vos]

Fix for JDK-8211362

Compile javafx-iio native files with -f-visibiliy=hidden in order
not to export the non-JNI symbols.
Although this issue was about libjavafx_iio.so only (and not about libjavafx_iio.a), this PR allows fixing the static build as well.

For static builds, we also use ld -r to build a static library, so that objcopy or similar can be used to remove the names of the
hidden symbols.

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Commit messages:
 - remove trailing whitespace
 - Fix for JDK-8211362

Changes: https://git.openjdk.java.net/jfx/pull/442/files
 Webrev: https://webrevs.openjdk.java.net/?repo=jfx&pr=442&range=00
  Issue: https://bugs.openjdk.java.net/browse/JDK-8211362
  Stats: 9 lines in 2 files changed: 5 ins; 0 del; 4 mod
  Patch: https://git.openjdk.java.net/jfx/pull/442.diff
  Fetch: git fetch https://git.openjdk.java.net/jfx pull/442/head:pull/442

PR: https://git.openjdk.java.net/jfx/pull/442