[ASan] Introduce a flag -asan-constructor-kind to control the generation of...

[ASan] Introduce a flag -asan-constructor-kind to control the generation of the Asan module constructor.

By default, ASan generates an asan.module_ctor function that initializes asan and
registers the globals in the module. This function is added to the
@llvm.global_ctors array. Previously, there was no way to control the
generation of this function.

This patch adds a way to control the generation of this function. The
flag -asan-constructor-kind has two options:

global: This is the default option and the default behavior of ASan. It generates an
asan.module_ctor function.
none: This skips the generation of the asan.module_ctor function.

rdar://104448572

Differential revision: https://reviews.llvm.org/D142505