RFR: JDK-8298908: Instrument Metaspace for ASan [v8]

[Justin King]

> This change instruments Metaspace for ASan. Metaspace allocates memory using `mmap`/`munmap` which ASan is not aware of. Fortunately ASan supports applications [manually poisoning/unpoisoning memory](https://github.com/google/sanitizers/wiki/AddressSanitizerManualPoisoning). ASan is able to detect poisoned memory, similar to `use-after-free`, and will raise an error similarly called `use-after-poison`. This provides and extra layer of defense and confidence.
> 
> The header `sanitizers/address.h` defines macros for poisoning/unpoisoning memory regions. These macros can be used regardless of build mode. When ASan is not available, they are implemented using a NOOP approach which still compiles the arguments but does so such that they will be stripped out by the compiler due to being unreachable. This helps with maintenance.
> 
> This also has the added benefit of making [LSan](https://bugs.openjdk.org/browse/JDK-8298445) more accurate and deterministic, as LSan will not look for pointers to malloc memory in poisoned memory regions.
> 
> IMO the benefit of doing this greatly outweighs the cost.

Justin King has updated the pull request incrementally with one additional commit since the last revision:

  Fix leading comment whitespace
  
  Signed-off-by: Justin King <jcking at google.com>

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Changes:
  - all: https://git.openjdk.org/jdk/pull/11702/files
  - new: https://git.openjdk.org/jdk/pull/11702/files/5ec30c8e..7e13768f

Webrevs:
 - full: https://webrevs.openjdk.org/?repo=jdk&pr=11702&range=07
 - incr: https://webrevs.openjdk.org/?repo=jdk&pr=11702&range=06-07

  Stats: 1 line in 1 file changed: 0 ins; 0 del; 1 mod
  Patch: https://git.openjdk.org/jdk/pull/11702.diff
  Fetch: git fetch https://git.openjdk.org/jdk pull/11702/head:pull/11702

PR: https://git.openjdk.org/jdk/pull/11702