...as passing (an upper bound on) the number of vector registers used in %al is
only required for variable-argument function calls, according to
<http://www.x86-64.org/documentation/abi.pdf> "System V Application Binary
Interface: AMD64 Architecture Processor Supplement, Draft Version 0.99.6."

Unclear why this got added in f424e55b
"INTEGRATION: CWS sixtyfour11," maybe on the basis of "doesn't hurt."

Change-Id: If6f8359d5bf6458274905d64adf82634bf90a24d