[clang][AArch32] Correctly align HA arguments when passed on the stack

Analogously to https://reviews.llvm.org/D98794 this patch uses the
`alignstack` attribute to fix incorrect passing of homogeneous
aggregate (HA) arguments on AArch32. The EABI/AAPCS was recently
updated to clarify how VFP co-processor candidates are aligned:
https://github.com/ARM-software/abi-aa/commit/4488e34998514dc7af5507236f279f6881eede62

Differential Revision: https://reviews.llvm.org/D100853