Fix -Xjitthreshold.

Previously, we'd always overwrite the user-supplied value because
the architecture-specific default gets set so late.

Bug: https://code.google.com/p/android/issues/detail?id=52017
Change-Id: I469bf9ce599820f5ce3dea346aa8f680deffb0c5

Bug: 8285558
Bug: https://code.google.com/p/android/issues/detail?id=52017
Change-Id: I28270f2573d46929eb10d30789fecf7d5a8cea75
Don't crash if the dmtracedump -d file doesn't exist.

Change-Id: Ie4b504b43a8a61d09ca60d68b1a62694391ac223
Check JavaVMAttachArgs::version in CheckJNI.

Bug: 8363798
Change-Id: I314bf6d5d64a1e27ad2c1580532133859031c623
pthread_create doesn't set errno.

Let's try to get slightly better logging and exception detail messages.

Also fix the "set but not read" warnings for the other pthread functions
in this file.

Bug: 8470684
Change-Id: I7f9dbb4d39b4e3022cd5f1a8a45c6426e68c858b
Track libcore DirectByteBuffer cleanup.

Bug: https://code.google.com/p/android/issues/detail?id=53637
Change-Id: I7acd990a2a48b41dacb5b09f6410b4634dd60438