Auto merge of #33414 - Nercury:master, r=alexcrichton

Add armv7-linux-androideabi target

This PR adds `armv7-linux-androideabi` target that matches `armeabi-v7a` Android ABI, ~~downscales `arm-linux-androideabi` target to match `armeabi` Android ABI~~ (TBD later if needed).

This should allow us to get the best performance from every [Android ABI level](http://developer.android.com/ndk/guides/abis.html).

Currently existing target `arm-linux-androideabi` started gaining features out of the supported range of [android `armeabi`](http://developer.android.com/ndk/guides/abis.html). While android compiler does not use a different target for later supported `armv7` architecture, it has distinct ABI name `armeabi-v7a`. We decided to add rust target `armv7-linux-androideabi` to match it.

Note that `NEON`, `VFPv3-D32`, and `ThumbEE` instruction sets are not added, because not all android devices are guaranteed to support all or some of these, and [their availability should be checked at runtime](http://developer.android.com/ndk/guides/abis.html#v7a).

~~This reduces performance of existing `arm-linux-androideabi` and may make it _much_ slower (we are talking more than order of magnitude in some random ad-hoc fp benchmark that I did).~~

Part of #33278.

src/doc/book/getting-started.md

@@ -98,6 +98,7 @@ unofficial locations.
 |  Target                       | std |rustc|cargo| notes                      |
 |-------------------------------|-----|-----|-----|----------------------------|
 | `aarch64-linux-android`       |  ✓  |     |     | ARM64 Android              |
+| `armv7-linux-androideabi`     |  ✓  |     |     | ARM-v7a Android            |
 | `i686-linux-android`          |  ✓  |     |     | 32-bit x86 Android         |
 | `i686-pc-windows-msvc` (XP)   |  ✓  |     |     | Windows XP support         |
 | `i686-unknown-freebsd`        |  ✓  |  ✓  |  ✓  | 32-bit FreeBSD             |