Print assert message after the "assertion failed" message instead of
printing it as a separate note. This makes the assert failure reporting
less verbose and also more useful to see the failure message inline with
the "assertion failed" message.

When record assertions fail, print an error message with the record's
location, so it's easier to see where the record that caused the assert
to fail was instantiated. This is useful when the assert condition in a
class depends on a template parameter, so we need to know the context of
the definition to determine why the assert failed.

Also enhanced the assert.td test to check for these context messages,
and also add checks for some assert failures that were missing in the
test.

This patch fixes two bugs that arise when a 'defm' inherits from a multiclass
and also from a class with assertions.

Differential Revision: https://reviews.llvm.org/D101626

This is step 3 of adding the 'assert' statement.

Differential Revision: https://reviews.llvm.org/D99751

This reverts commit 3b9a15d910a8c748b1444333a4a3905a996528bc.

Differential Revision: https://reviews.llvm.org/D99275

Differential Revision: https://reviews.llvm.org/D93911

This first step adds the assert statement and supports it at top level
and in record definitions. Later steps will support it in class
definitions and multiclasses.