Also use -mno-thumb for 32-bit ARM

Author: encukou

Doc/using/configure.rst

@@ -789,7 +789,7 @@ also be used to improve performance.
 
    - ``-fno-omit-frame-pointer`` and/or ``-mno-omit-leaf-frame-pointer``
      are added when the compiler supports them,
-   - ``-marm`` is added on 32-bit ARM when supported,
+   - ``-marm`` and/or ``-mno-thumb`` is added on 32-bit ARM when supported,
    - on s390x platforms, when supported, ``-mbackchain`` is added *instead*
      of the above frame pointer flags
 

configure

@@ -2549,9 +2549,13 @@ AS_VAR_IF([ac_cv_gcc_compat], [yes], [
         frame_pointer_cflags="$frame_pointer_cflags -mno-omit-leaf-frame-pointer"
       ], [], [-Werror])
       AS_CASE([$host_cpu], [arm|armv*], [
+        dnl GCC uses "-marm"; clang uses "-mno-thumb"
         AX_CHECK_COMPILE_FLAG([-marm], [
           frame_pointer_cflags="$frame_pointer_cflags -marm"
         ], [], [-Werror])
+        AX_CHECK_COMPILE_FLAG([-mno-thumb], [
+          frame_pointer_cflags="$frame_pointer_cflags -mno-thumb"
+        ], [], [-Werror])
       ])
       AS_CASE([$host_cpu], [s390*], [
         AX_CHECK_COMPILE_FLAG([-mbackchain], [