Reorder the TOC so that targets are put under their meta-group

Author: Lokathor

src/doc/rustc/src/SUMMARY.md

@@ -30,10 +30,15 @@
     - [aarch64-nintendo-switch-freestanding](platform-support/aarch64-nintendo-switch-freestanding.md)
     - [armeb-unknown-linux-gnueabi](platform-support/armeb-unknown-linux-gnueabi.md)
     - [arm-none-eabi](platform-support/arm-none-eabi.md)
-    - [armv4t-none-eabi](platform-support/armv4t-none-eabi.md)
-    - [armv5te-none-eabi](platform-support/armv5te-none-eabi.md)
-    - [armv7r-none-eabi](platform-support/armv7r-none-eabi.md)
-    - [armv8r-none-eabihf](platform-support/armv8r-none-eabihf.md)
+      - [armv4t-none-eabi](platform-support/armv4t-none-eabi.md)
+      - [armv5te-none-eabi](platform-support/armv5te-none-eabi.md)
+      - [armv7r-none-eabi](platform-support/armv7r-none-eabi.md)
+      - [armv8r-none-eabihf](platform-support/armv8r-none-eabihf.md)
+      - [thumbv6m-none-eabi](./platform-support/thumbv6m-none-eabi.md)
+      - [thumbv7em-none-eabi\*](./platform-support/thumbv7em-none-eabi.md)
+      - [thumbv7m-none-eabi](./platform-support/thumbv7m-none-eabi.md)
+      - [thumbv8m.base-none-eabi](./platform-support/thumbv8m.base-none-eabi.md)
+      - [thumbv8m.main-none-eabi\*](./platform-support/thumbv8m.main-none-eabi.md)
     - [armv6k-nintendo-3ds](platform-support/armv6k-nintendo-3ds.md)
     - [armv7-sony-vita-newlibeabihf](platform-support/armv7-sony-vita-newlibeabihf.md)
     - [armv7-unknown-linux-uclibceabi](platform-support/armv7-unknown-linux-uclibceabi.md)
@@ -60,11 +65,6 @@
     - [riscv32imac-unknown-xous-elf](platform-support/riscv32imac-unknown-xous-elf.md)
     - [riscv32*-unknown-none-elf](platform-support/riscv32-unknown-none-elf.md)
     - [sparc-unknown-none-elf](./platform-support/sparc-unknown-none-elf.md)
-    - [thumbv6m-none-eabi](./platform-support/thumbv6m-none-eabi.md)
-    - [thumbv7m-none-eabi](./platform-support/thumbv7m-none-eabi.md)
-    - [thumbv7em-none-eabi\*](./platform-support/thumbv7em-none-eabi.md)
-    - [thumbv8m.base-none-eabi](./platform-support/thumbv8m.base-none-eabi.md)
-    - [thumbv8m.main-none-eabi\*](./platform-support/thumbv8m.main-none-eabi.md)
     - [*-pc-windows-gnullvm](platform-support/pc-windows-gnullvm.md)
     - [\*-nto-qnx-\*](platform-support/nto-qnx.md)
     - [*-unikraft-linux-musl](platform-support/unikraft-linux-musl.md)