configure: remove unnecessary subshell

Do not use a subshell to hide the shadowing of $config_host_mak.

Reviewed-by: Philippe Mathieu-Daudé <philmd@linaro.org>
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>

configure

@@ -1671,10 +1671,9 @@ if test "$targetos" = windows; then
 fi
 
 # tests/tcg configuration
-(config_host_mak=tests/tcg/config-host.mak
 mkdir -p tests/tcg
-echo "# Automatically generated by configure - do not modify" > $config_host_mak
-echo "SRC_PATH=$source_path" >> $config_host_mak
+echo "# Automatically generated by configure - do not modify" > tests/tcg/$config_host_mak
+echo "SRC_PATH=$source_path" >> tests/tcg/$config_host_mak
 
 tcg_tests_targets=
 for target in $target_list; do
@@ -1717,9 +1716,8 @@ for target in $target_list; do
 done
 
 if test "$tcg" = "enabled"; then
-    echo "TCG_TESTS_TARGETS=$tcg_tests_targets" >> config-host.mak
+    echo "TCG_TESTS_TARGETS=$tcg_tests_targets" >> $config_host_mak
 fi
-)
 
 if test "$skip_meson" = no; then
   cross="config-meson.cross.new"