Bug 1381741 - Only fail gold detection when --enable-gold is specified; r=glandium

developer_options (!--enable-release) implies to search for and prefer
the gold linker. As part of porting gold detection to moz.configure
in d0e782180741 (bug 1351109), the logic inadvertently changed to
require gold when either --enable-gold or !--enable-release were
present.

This commit relaxes the requirement to find gold when only --enable-gold
is true.

MozReview-Commit-ID: HTBicWNUkvy

--HG--
extra : rebase_source : dd3938a7914f5db6c315fb775e7cc5ea177bf600

build/moz.configure/toolchain.configure

@@ -1105,18 +1105,19 @@ def enable_gold(enable_gold_option, c_compiler, developer_options, build_env):
     # Used to check the kind of linker
     version_check = ['-Wl,--version']
     cmd_base = c_compiler.wrapper + [c_compiler.compiler] + c_compiler.flags
-    if enable_gold_option or developer_options:
+
+    def resolve_gold():
         # Try to force the usage of gold
         targetDir = os.path.join(build_env.topobjdir, 'build', 'unix', 'gold')
 
         gold_detection_arg = '-print-prog-name=ld.gold'
         gold = check_cmd_output(c_compiler.compiler, gold_detection_arg).strip()
         if not gold:
-            die('Could not find gold')
+            return
 
         goldFullPath = find_program(gold)
         if goldFullPath is None:
-            die('Could not find gold')
+            return
 
         if os.path.exists(targetDir):
             shutil.rmtree(targetDir)
@@ -1135,6 +1136,16 @@ def enable_gold(enable_gold_option, c_compiler, developer_options, build_env):
             # The -B trick didn't work, removing the directory
             shutil.rmtree(targetDir)
 
+    if enable_gold_option or developer_options:
+        result = resolve_gold()
+
+        if result:
+            return result
+        # gold is only required if --enable-gold is used.
+        elif enable_gold_option:
+            die('Could not find gold')
+        # Else fallthrough.
+
     cmd = cmd_base + version_check
     cmd_output = check_cmd_output(*cmd).decode('utf-8')
     # using decode because ld can be localized and python will