branches: 1.2.4;
t_signal_and_sp: Check sp on elf constructor/destructor entry too.

XXX Should maybe test both .ctors/.dtors and .init/fini_array, but
for now I'm limiting this to whatever gcc uses by default for each
architecture.

PR kern/59327: user stack pointer is not aligned properly

Test stack pointer alignment in various scenarios.

1. elf entry point
2. main function
3. signal handler

Extend the test to amd64 while here -- fortunately both aarch64 and
amd64 pass, but others, such as mips, will fail:

PR kern/59327: user stack pointer is not aligned properly

This extends the test that was previously written for:

PR kern/58149: aarch64: Cannot return from a signal handler if SP was
misaligned when the signal arrived

With any luck, this will help us to systematically eradicate misaligned
stack pointers as hypothesized to be the reason for:

PR port-mips/59236: Multiple segfaults in erlite3 boot