Change /build to /build* in top-level .gitignore

[dyung]

Summary

Internally our build scripts create build directories of the form build-<branch info> so it would be useful if the top level .gitignore file ignored build* instead of just build so that git would ignore them. We have had this privately for quite a while, but it seems like it could be something that might be useful upstream in case anyone else does something similar.

[dyung]

Adding James and Chris as reviews as it was suggested they might have an interest in this change.

[beanz]

Yes please! I actually have this locally.

.gitignore

 *.pyc
 # vim swap files
 .*.sw?
 .sw?
 #OS X specific files.
 .DS_store
 
 # Nested build directory
-/build
+/build*
 
 #==============================================================================#
 # Explicit files to ignore (only matches one).
 #==============================================================================#
 # Various tag programs
 /tags
 /TAGS
 /GPATH

 #==============================================================================#
 # Directories to ignore (do not add trailing '/'s, they skip symlinks).
 #==============================================================================#
 # VS2017 and VSCode config files.
 .vscode
 .vs
 # clangd index
 .clangd
 No newline at end of file