configure: Don't run Xen compile checks in subshells

The Xen compile checks are currently run inside subshells. This
is unnecessary and has the effect that if do_cc() exits with
an error message then this only causes the subshell to exit,
not the whole of configure, which is confusing. Remove the
subshells, changing:
  if ( cat ; compile_prog ) ; then ...
to
  if cat && compile_prog ; then ...
Signed-off-by: NPeter Maydell <peter.maydell@linaro.org>
Signed-off-by: NBlue Swirl <blauwirbel@gmail.com>

configure

@@ -1396,8 +1396,8 @@ EOF
     xen=no
 
   # Xen unstable
-  elif (
-      cat > $TMPC <<EOF
+  elif
+      cat > $TMPC <<EOF &&
 #include <xenctrl.h>
 #include <xenstore.h>
 #include <stdint.h>
@@ -1417,12 +1417,12 @@ int main(void) {
 }
 EOF
       compile_prog "" "$xen_libs"
-    ) ; then
+    then
     xen_ctrl_version=420
     xen=yes
 
-  elif (
-      cat > $TMPC <<EOF
+  elif
+      cat > $TMPC <<EOF &&
 #include <xenctrl.h>
 #include <xs.h>
 #include <stdint.h>
@@ -1441,13 +1441,13 @@ int main(void) {
 }
 EOF
       compile_prog "" "$xen_libs"
-    ) ; then
+    then
     xen_ctrl_version=410
     xen=yes
 
   # Xen 4.0.0
-  elif (
-      cat > $TMPC <<EOF
+  elif
+      cat > $TMPC <<EOF &&
 #include <xenctrl.h>
 #include <xs.h>
 #include <stdint.h>
@@ -1468,13 +1468,13 @@ int main(void) {
 }
 EOF
       compile_prog "" "$xen_libs"
-    ) ; then
+    then
     xen_ctrl_version=400
     xen=yes
 
   # Xen 3.4.0
-  elif (
-      cat > $TMPC <<EOF
+  elif
+      cat > $TMPC <<EOF &&
 #include <xenctrl.h>
 #include <xs.h>
 int main(void) {
@@ -1490,13 +1490,13 @@ int main(void) {
 }
 EOF
       compile_prog "" "$xen_libs"
-    ) ; then
+    then
     xen_ctrl_version=340
     xen=yes
 
   # Xen 3.3.0
-  elif (
-      cat > $TMPC <<EOF
+  elif
+      cat > $TMPC <<EOF &&
 #include <xenctrl.h>
 #include <xs.h>
 int main(void) {
@@ -1508,7 +1508,7 @@ int main(void) {
 }
 EOF
       compile_prog "" "$xen_libs"
-    ) ; then
+    then
     xen_ctrl_version=330
     xen=yes