.gitignore: Ignore build tools build logs

The python BaseTools/Edk2ToolsBuild.py creates files in
BaseTools/BaseToolsBuild and should be ignored.

Change-Id: I9af2f9a798858087ef6b69d72d58433ee65ae6e3
Signed-off-by: Jeff Brasen <jbrasen@nvidia.com>
Reviewed-by: Liming Gao <gaoliming@byosoft.com.cn>
Reviewed-on: https://git-master.nvidia.com/r/c/3rdparty/edk2/+/2738035
Reviewed-by: svc-sw-mobile-l4t <svc-sw-mobile-l4t@nvidia.com>
Reviewed-by: svcacv <svcacv@nvidia.com>
GVS: Gerrit_Virtual_Submit

BaseTools/.gitignore

@@ -17,4 +17,5 @@ Source/C/VfrCompile/VfrTokens.h
 Source/C/bin/
 Source/C/libs/
 Bin/Win32
-Lib
+Lib
+BaseToolsBuild/