[android] Disable LLVM JIT HAL driver related tests (#2632)

We don't want LLVM JIT as part of the IREE runtime when on Android.
This commit serves as the first step as disabling it by turning
off tests.

Along the way, made the compiler target backend names consistent
with what's used elsewhere.

Progress on https://github.com/google/iree/issues/2528
diff --git a/docs/get_started/cmake_options_and_variables.md b/docs/get_started/cmake_options_and_variables.md
index 8e121fc..3f3dbdd 100644
--- a/docs/get_started/cmake_options_and_variables.md
+++ b/docs/get_started/cmake_options_and_variables.md
@@ -63,17 +63,21 @@
 
 #### `IREE_HAL_DRIVERS_TO_BUILD`:STRING
 
-*This does not have any effect at the moment, but will be supported in the
-future!* Semicolon-separated list of HAL drivers to build, or `all` for building
-all HAL drivers. Case-insensitive. Defaults to `all`. Example:
+*Righ now this only affects whether tests are enabled when compiling for
+Android; it will be fully supported in the future!*
+
+Semicolon-separated list of HAL drivers to build, or `all` for building all HAL
+drivers. Case-insensitive. Defaults to `all`. Example:
 `-DIREE_HAL_DRIVERS_TO_BUILD="Vulkan;VMLA"`.
 
 #### `IREE_TARGET_BACKENDS_TO_BUILD`:STRING
 
-*This does not have any effect at the moment, but will be supported in the
-future!* Semicolon-separated list of HAL drivers to build, or `all` for building
-all HAL drivers. Case-insensitive. Defaults to `all`. Example:
-`-DIREE_HAL_DRIVERS_TO_BUILD="Vulkan_SPIRV;VMLA"`.
+*Righ now this only affects whether tests are enabled when compiling for
+Android; it will be fully supported in the future!*
+
+Semicolon-separated list of HAL drivers to build, or `all` for building all
+compiler target backends. Case-insensitive. Defaults to `all`. Example:
+`-DIREE_HAL_DRIVERS_TO_BUILD="Vulkan-SPIRV;VMLA"`.
 
 #### `IREE_ENABLE_LLD`:BOOL