RFR: 8068736: Avoid synchronization on Executable/Field.declaredAnnotations

[Claes Redestad]

Hi,

please review this patch to use double-checked locking to avoid
synchronization overhead on repeated access to the
declaredAnnotations field in Executable and Field.

webrev: http://cr.openjdk.java.net/~redestad/8068736/webrev.00
bug: https://bugs.openjdk.java.net/browse/JDK-8068736

Testing: jtreg java/lang

Benchmarking:
- no significant changes in a small set of SPEC benchmarks
- up to 4x in micros focused on repeated access to the
declaredAnnotations field, both in single- and multithreaded setups
- less than 5% cost (not statistically significant) on micros accessing
the declaredAnnotation map of a method only once.

/Claes