Rollup merge of rust-lang#37482 - matwey:configure-arm, r=alexcrichton

Misc fixes for configure

Currently,
`./configure` at armv6 machines ends up with

```
configure: error: unknown CPU type: armv6l
```

`./configure` at armv7 machines **silently** produces build for armv6 (compatible, but suboptimal)

```
configure: CFG_BUILD            := arm-unknown-linux-gnueabihf
```

Author: Jonathan Turner

configure

@@ -507,11 +507,16 @@ case $CFG_CPUTYPE in
         CFG_CPUTYPE=arm
         ;;
 
-    armv7l)
+    armv6l)
         CFG_CPUTYPE=arm
         CFG_OSTYPE="${CFG_OSTYPE}eabihf"
         ;;
 
+    armv7l)
+        CFG_CPUTYPE=armv7
+        CFG_OSTYPE="${CFG_OSTYPE}eabihf"
+        ;;
+
     aarch64)
         CFG_CPUTYPE=aarch64
         ;;