Disable ftrace on arm32

This is required to link the ARM kernel. For details see
ClangBuiltLinux/linux#35.

Signed-off-by: Joel Stanley <joel@jms.id.au>

driver.sh

@@ -168,6 +168,8 @@ build_linux() {
     cat ../configs/common.config >> .config
     # Some torture test configs cause issues on x86_64
     [[ $ARCH != "x86_64" ]] && cat ../configs/tt.config >> .config
+    # Disable ftrace on arm32: https://github.com/ClangBuiltLinux/linux/issues/35
+    [[ $ARCH == "arm" ]] && ./scripts/config -d CONFIG_FTRACE
   fi
   # Make sure we build with CONFIG_DEBUG_SECTION_MISMATCH so that the
   # full warning gets printed and we can file and fix it properly.