scons: Build src/mesa/main/es1_conversion.c for all builds.

Signed-off-by: Vinson Lee <vlee@freedesktop.org>
diff --git a/src/mesa/SConscript b/src/mesa/SConscript
index 11e034f..4c3355b 100644
--- a/src/mesa/SConscript
+++ b/src/mesa/SConscript
@@ -65,6 +65,7 @@
     'main/enable.c',
     'main/enums.c',
     'main/errors.c',
+    'main/es1_conversion.c',
     'main/eval.c',
     'main/execmem.c',
     'main/extensions.c',
@@ -338,7 +339,7 @@
     enabled_apis += ['ES1', 'ES2']
 
     # generate GLES sources
-    gles_sources = ['main/es1_conversion.c',]
+    gles_sources = []
 
     # generate GLES headers
     gles_headers = []