SL-16040: Honor autobuild_{configure,build}_parameters variables.

The generic build.sh script honors these environment variables to specify
parameters to the autobuild configure and autobuild build steps, respectively.
Support them in the viewer-specific build.sh too.

In the generic build.sh, autobuild_configure_parameters allows specifying
command-line switches either for autobuild or, following --, for the
underlying tool (in our case, CMake). In order to support that variable the
same way here, we insert -- (as before) when autobuild_configure_parameters is
unset or empty, since the rest of the switches *we* specify are for CMake.

That means that, as with the generic build.sh, a non-empty
autobuild_configure_parameters override must precede any switches intended for
CMake with the -- separator.

build.sh

@@ -132,7 +132,11 @@ pre_build()
     fi
     set -x
 
-    "$autobuild" configure --quiet -c $variant -- \
+    # honor autobuild_configure_parameters same as sling-buildscripts
+    eval_autobuild_configure_parameters=$(eval $(echo echo $autobuild_configure_parameters))
+
+    "$autobuild" configure --quiet -c $variant \
+     ${eval_autobuild_configure_parameters:---} \
      -DPACKAGE:BOOL=ON \
      -DHAVOK:BOOL="$HAVOK" \
      -DRELEASE_CRASH_REPORTING:BOOL="$RELEASE_CRASH_REPORTING" \
@@ -182,7 +186,11 @@ build()
   if $build_viewer
   then
     begin_section "autobuild $variant"
-    "$autobuild" build --no-configure -c $variant || fatal "failed building $variant"
+    # honor autobuild_build_parameters same as sling-buildscripts
+    eval_autobuild_build_parameters=$(eval $(echo echo $autobuild_build_parameters))
+    "$autobuild" build --no-configure -c $variant \
+         $eval_autobuild_build_parameters \
+    || fatal "failed building $variant"
     echo true >"$build_dir"/build_ok
     end_section "autobuild $variant"