Fix armv7a on Android "end-of-support" build and documentation

* Only print a warning for this build
* Fix the wording in documentation to avoid misunderstanding. User can
  still run armv7a on Android, but we stop testing it and this build is
  discouraged

Resolves COMPMID-5379

Signed-off-by: SiCong Li <sicong.li@arm.com>
Change-Id: I3d00baa2479671bcef8882db0e3d3cc3043d5811
Reviewed-on: https://review.mlplatform.org/c/ml/ComputeLibrary/+/7838
Tested-by: Arm Jenkins <bsgcomp@arm.com>
Benchmark: Arm Jenkins <bsgcomp@arm.com>
Reviewed-by: Gunes Bayir <gunes.bayir@arm.com>
Comments-Addressed: Arm Jenkins <bsgcomp@arm.com>
diff --git a/SConstruct b/SConstruct
index 890c519..be438e0 100644
--- a/SConstruct
+++ b/SConstruct
@@ -169,8 +169,7 @@
 Help(vars.GenerateHelpText(env))
 
 if 'armv7a' in env['arch'] and env['os'] == 'android':
-    print("armv7a is not supported on Android")
-    Exit(1)
+    print("WARNING: armv7a on Android is no longer maintained")
 
 if env['linker_script'] and env['os'] != 'bare_metal':
     print("Linker script is only supported for bare_metal builds")