build: unbreak ustack on smartos

I disabled the -ffunction-sections and -fdata-sections switches in 202df30
because they're horribly buggy with some gcc/binutils combos.

However, it turns out that the dtrace/ustack post-processing tool requires
that V8 is compiled with said switches and was broken because of it.

This commit turns them on again on SunOS systems. Let's hope for the best.

common.gypi

@@ -46,18 +46,25 @@
       },
       'Release': {
         'conditions': [
+          ['target_arch=="x64"', {
+            'msvs_configuration_platform': 'x64',
+          }],
           ['node_unsafe_optimizations==1', {
             'cflags': [ '-O3', '-ffunction-sections', '-fdata-sections' ],
             'ldflags': [ '-Wl,--gc-sections' ],
           }, {
             'cflags': [ '-O2', '-fno-strict-aliasing', '-fno-tree-vrp' ],
-            'cflags!': [ '-O3',
-                         '-fstrict-aliasing',
-                         '-ffunction-sections',
-                         '-fdata-sections' ],
+            'cflags!': [ '-O3', '-fstrict-aliasing' ],
+            'conditions': [
+              # Required by the dtrace post-processor. Unfortunately,
+              # some gcc/binutils combos generate bad code when
+              # -ffunction-sections is enabled. Let's hope for the best.
+              ['OS=="solaris"', {
+                'cflags': [ '-ffunction-sections', '-fdata-sections' ],
+              }, {
+                'cflags!': [ '-ffunction-sections', '-fdata-sections' ],
               }],
-          ['target_arch=="x64"', {
-            'msvs_configuration_platform': 'x64',
+            ],
           }],
           ['OS=="solaris"', {
             'cflags': [ '-fno-omit-frame-pointer' ],