Don't use lld linker with memcheck

The switch to lld caused many new violations.
The ones for MSan are being handled upstream: crbug.com/772559
But memcheck is unlikely to be supported.

BUG=webrtc:8356
TBR=kjellander@webrtc.org

Change-Id: I6b728b7d689a1d883fc6e49eb438336bda08afe1
Reviewed-on: https://webrtc-review.googlesource.com/7080
Commit-Queue: Oleh Prypin <oprypin@webrtc.org>
Reviewed-by: Oleh Prypin <oprypin@webrtc.org>
Cr-Commit-Position: refs/heads/master@{#20195}

tools_webrtc/mb/mb_config.pyl

@@ -261,7 +261,8 @@
       'x64', 'no_rtc_tests'
     ],
     'memcheck_release_bot_x64': [
-      'memcheck', 'gn', 'openh264_release_bot', 'x64', 'use_default_libcxx'
+      'memcheck', 'gn', 'openh264_release_bot', 'x64', 'use_default_libcxx',
+      'no_lld'
     ],
 
     # iOS
@@ -430,6 +431,10 @@
       'gn_args': 'is_clang=false',
     },
 
+    'no_lld': {
+      'gn_args': 'use_lld=false',
+    },
+
     'no_rtc_tests': {
       'gn_args': 'rtc_include_tests=false',
     },