amp-toolbox does not build on Windows

Windows 10 64bit (Version 1909)
node.js 12.16.0
npm 6.13.4

`npm run build`
```
lerna ERR! npm run build exited 2 in '@ampproject/toolbox-linter'
lerna ERR! npm run build stdout:

> @ampproject/toolbox-linter@2.0.1 build C:\Users\mdmower\source\amp-toolbox\packages\linter
> tsc --resolveJsonModule --module commonjs --target es2018 --esModuleInterop --strictNullChecks --declaration --outDir dist src/*.ts

error TS6053: File 'src/*.ts' not found.

lerna ERR! npm run build stderr:
npm ERR! code ELIFECYCLE
npm ERR! errno 2
npm ERR! @ampproject/toolbox-linter@2.0.1 build: `tsc --resolveJsonModule --module commonjs --target es2018 --esModuleInterop --strictNullChecks --declaration --outDir dist src/*.ts`
npm ERR! Exit status 2
npm ERR!
npm ERR! Failed at the @ampproject/toolbox-linter@2.0.1 build script.
```

Start with the @ampproject/toolbox-linter build entry point and the `tsc` command shown in the issue, focusing on how `src/*.ts` is resolved on Windows. Run `npm run build` on Windows 10 and confirm that the toolbox builds successfully without the TS6053 error.

Written by the indexing model from the issue text.