Auto merge of #49774 - danc86:configure.py-tools, r=alexcrichton
Auto merge of #49774 - danc86:configure.py-tools, r=alexcrichton

configure.py --tools should set a list instead of a string

Currently the --tools option does not work because it is setting a string value
for 'build.tools'. It should be a list of strings instead.

aidancully/rust,aidancully/rust,GBGamer/rust,GBGamer/rust,graydon/rust,aidancully/rust,graydon/rust,graydon/rust,aidancully/rust,aidancully/rust,graydon/rust,GBGamer/rust,GBGamer/rust,graydon/rust,GBGamer/rust,graydon/rust,GBGamer/rust,GBGamer/rust,GBGamer/rust,aidancully/rust