An Ubuntu 18 system's libc, even with older gcc versions 4.8 (we did not try < 4.5), decided to callee-save a xmm register on the stack. This patch aligns the stack in the function in the test that is calling vfprintf. This problem generally affects all functions that we are hand-coding in asm and calling from a test. Absent a complete review of all hand-coded functions in the code base, this fixes this one only single case where a test failure was observed.
Fixes #3674 (closed)