detect/guess arm32 platform (unsupported);

--- a/lib/scripts/isabelle-platform	Sat Oct 03 15:11:30 2020 +0200
+++ b/lib/scripts/isabelle-platform	Sat Oct 03 19:56:02 2020 +0200
@@ -16,6 +16,9 @@
       aarch64)
         ISABELLE_PLATFORM64=arm64-linux
         ;;
+      arm*)
+        ISABELLE_PLATFORM32=arm32-linux
+        ;;
       *)
         ISABELLE_PLATFORM32=x86-linux
         ISABELLE_PLATFORM64=x86_64-linux

--- a/src/Pure/System/platform.scala	Sat Oct 03 15:11:30 2020 +0200
+++ b/src/Pure/System/platform.scala	Sat Oct 03 19:56:02 2020 +0200
@@ -39,12 +39,14 @@
   private val X86 = """i.86|x86""".r
   private val X86_64 = """amd64|x86_64""".r
   private val Arm64 = """arm64|aarch64""".r
+  private val Arm32 = """arm""".r
 
   def cpu_arch: String =
     System.getProperty("os.arch", "") match {
       case X86() => "x86"
       case X86_64() => "x86_64"
       case Arm64() => "arm64"
+      case Arm32() => "arm32"
       case _ => error("Failed to determine CPU architecture")
     }