Fixes a small mistake in the definitions of assert alias assert_ptr_null

[Ivan-Kouznetsov]

This fixes a small mistake in the definitions of assert aliases.
munit_assert_null_equal is not defined, assert_ptr_null should refer to munit_assert_ptr_null which is defined

[Ivan-Kouznetsov]

The check failed due to the VM on which the check was done not having the compiler specified in the makefile:
make: pgcc: Command not found