rts: Non-portable pthread related code for NetBSD
Add NetBSD-specific code for non-portable parts of rts.
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are either individually buildable or squashed -
have commit messages which describe what they do (referring to [Notes][notes] and tickets using #NNNN
syntax when appropriate) -
have added source comments describing your change. For larger changes you likely should add a [Note][notes] and cross-reference it from the relevant places. -
add a testcase to the testsuite. -
replace this message with a description motivating your change
Edited by PHO