SERVER-13724 Add --disable-warnings-as-errors scons option

This change was prompted by attempts to build 2.6.0 in SLES 10 with
its system gcc version 4.1.2. It builds fine other than a sole
warning - src/third_party/boost/boost/thread/detail/thread.hpp:316:
warning: type attributes are honored only at type definition. It
should also help in cases where compilers are too new.
(cherry picked from commit 27c128d)

Conflicts:

	SConstruct

Author: ehershey

SConstruct

@@ -231,6 +231,8 @@ add_option("mongod-concurrency-level", "Concurrency level, \"global\" or \"db\""
 add_option('client-dist-basename', "Name of the client source archive.", 1, False,
            default='mongo-cxx-driver')
 
+add_option('disable-warnings-as-errors', "Don't add -Werror to compiler command line", 0, False)
+
 # don't run configure if user calls --help
 if GetOption('help'):
     Return()
@@ -710,7 +712,9 @@ if nix:
                          "-Winvalid-pch"] )
     # env.Append( " -Wconversion" ) TODO: this doesn't really work yet
     if linux:
-        env.Append( CCFLAGS=["-Werror", "-pipe"] )
+        env.Append( CCFLAGS=["-pipe"] )
+        if not has_option("disable-warnings-as-errors"):
+            env.Append( CCFLAGS=["-Werror"] )
         if not has_option('clang'):
             env.Append( CCFLAGS=["-fno-builtin-memcmp"] ) # glibc's memcmp is faster than gcc's