Allow opting out of thumb mode for ARM builds.

build/config/arm.gni

Index: build/config/arm.gni
diff --git a/build/config/arm.gni b/build/config/arm.gni
index 2ea36fec4351183d397571a70291f3acbdd663d9..85565aafc4d5bebea32ba764ffc9ab4aa52284c0 100644
--- a/build/config/arm.gni
+++ b/build/config/arm.gni
@@ -28,6 +28,10 @@ if (target_cpu == "arm" || current_cpu == "arm") {
 
     # Whether to enable optional NEON code paths.
     arm_optionally_use_neon = false
+
+    # Thumb is a reduced instruction set available on some ARM processors that
+    # has increased code density.
+    arm_use_thumb = true
   }
 
   assert(arm_float_abi == "" || arm_float_abi == "hard" ||
@@ -42,9 +46,6 @@ if (target_cpu == "arm" || current_cpu == "arm") {
       arm_float_abi = "softfp"
     }
     arm_fpu = "vfp"
-
-    # Thumb is a reduced instruction set available on some ARM processors that
-    # has increased code density.
     arm_use_thumb = false
   } else if (arm_version == 7) {
     arm_arch = "armv7-a"
@@ -60,8 +61,6 @@ if (target_cpu == "arm" || current_cpu == "arm") {
       }
     }
 
-    arm_use_thumb = true
-
     if (arm_use_neon) {
       arm_fpu = "neon"
     } else {
@@ -81,8 +80,6 @@ if (target_cpu == "arm" || current_cpu == "arm") {
       }
     }
 
-    arm_use_thumb = true
-
     if (arm_use_neon) {
       arm_fpu = "neon"
     } else {