drmemory 2.6.19984/cronbuild on Win10/Workstation on IBM 7945/XEON crashes with ASSERT FAILURE

**Describe the bug**
drmemory crashes with the following assertion:
---- snip ----
```
$ drmemory -debug -- myhorribleapp.exe
~~Dr.M~~ Dr. Memory version 2.6.19984
~~Dr.M~~ Running "C:\myhorribleapp.exe"
~~Dr.M~~ Using system call file C:\Users\roland_mainz\AppData\Roaming\Dr. Memory\symcache\syscalls_x64.txt
~~Dr.M~~ ERROR: Failed to find "main" for limiting memory dump
ASSERT FAILURE
D:\a\drmemory\drmemory\ext\drx\scatter_gather_x86.c:122: proc_avx_enabled() (Scatter/gather instrs not available)
```
---- snip ----

**To Reproduce**
Steps to reproduce the behavior:
1. Get a IBM 7945/XEON machine
2. Install Win10/Workstation on it
3. $ bcdedit.exe /set nx AlwaysOff ## (just to be sure)
4. Run any app with $ drmemory -debug -- myhorribleapp.exe

**Expected behaviour**
drmemory works

** Actual behaviour:
Crash

**Versions**
- Windows version:
Microsoft Windows [Version 10.0.19045.4894]
- What version of Dr. Memory are you using?
$ drmemory -version
Dr. Memory version 2.6.19984 -- build 0
- Does the latest build from
https://drmemory.org/page_download.html#sec_latest_build solve the problem?
No
- Is your application 32-bit or 64-bit?
64bit