configure: Override the os default with --disable-pie

Some distributions, e.g. Ubuntu 19.10, enable PIE by default.
If for some reason one wishes to build a non-pie binary, we
must provide additional options to override.

At the same time, reorg the code to an elif chain.
Reviewed-by: NAlex Bennée <alex.bennee@linaro.org>
Reviewed-by: NPhilippe Mathieu-Daudé <philmd@redhat.com>
Reviewed-by: NThomas Huth <thuth@redhat.com>
Signed-off-by: NRichard Henderson <richard.henderson@linaro.org>
---
v3: Update for QEMU_LDFLAGS.

configure

@@ -2124,19 +2124,18 @@ if compile_prog "-Werror -fno-pie" "-no-pie"; then
   LDFLAGS_NOPIE="-no-pie"
 fi
 
-if test "$pie" != "no" ; then
-  if compile_prog "-fPIE -DPIE" "-pie"; then
-    QEMU_CFLAGS="-fPIE -DPIE $QEMU_CFLAGS"
-    QEMU_LDFLAGS="-pie $QEMU_LDFLAGS"
-    pie="yes"
-  else
-    if test "$pie" = "yes"; then
-      error_exit "PIE not available due to missing toolchain support"
-    else
-      echo "Disabling PIE due to missing toolchain support"
-      pie="no"
-    fi
-  fi
+if test "$pie" = "no"; then
+  QEMU_CFLAGS="$CFLAGS_NOPIE $QEMU_CFLAGS"
+  QEMU_LDFLAGS="$LDFLAGS_NOPIE $QEMU_LDFLAGS"
+elif compile_prog "-fPIE -DPIE" "-pie"; then
+  QEMU_CFLAGS="-fPIE -DPIE $QEMU_CFLAGS"
+  QEMU_LDFLAGS="-pie $QEMU_LDFLAGS"
+  pie="yes"
+elif test "$pie" = "yes"; then
+  error_exit "PIE not available due to missing toolchain support"
+else
+  echo "Disabling PIE due to missing toolchain support"
+  pie="no"
 fi
 
 # Detect support for PT_GNU_RELRO + DT_BIND_NOW.