border-radius CSS property doesn't affect <select>s in some browsers.
Hence, @input-border-radius doesn't affect <select class="form-control"> in some browsers.
Closes #15340.
[skip sauce]
[skip validator]
// TODO: Rename `@input-border-radius` to `@input-border-radius-base` in v4
//** Default `.form-control` border radius
+// This has no effect on `<select>`s in some browsers, due to the limited stylability of `<select>`s in CSS.
@input-border-radius: @border-radius-base;
//** Large `.form-control` border radius
@input-border-radius-large: @border-radius-large;