Bug 1086705: Disable -Werror=switch, r=froydnj, a=RyanVM

Gecko, for better or worse, allows non-m-c apps to define custom error codes and
use them in nsresult. This error breaks the ability to switch on those custom
error codes when an error happens. For this reason, it's not reasonable to make
this an error at present.

configure.in

@@ -1536,7 +1536,6 @@ if test "$GNU_CXX"; then
     # -Wreturn-type - catches missing returns, zero false positives
     # -Wsequence-point - catches undefined order behavior like `a = a++`
     # -Wsign-compare - catches comparison of signed and unsigned types
-    # -Wswitch - catches switches without all enum cases or default case
     # -Wtrigraphs - catches unlikely use of trigraphs
     # -Wtype-limits - catches overflow bugs, few false positives
     # -Wunused-label - catches unused goto labels
@@ -1555,7 +1554,6 @@ if test "$GNU_CXX"; then
     _WARNINGS_CXXFLAGS="${_WARNINGS_CXXFLAGS} -Werror=pointer-arith"
     _WARNINGS_CXXFLAGS="${_WARNINGS_CXXFLAGS} -Werror=return-type"
     _WARNINGS_CXXFLAGS="${_WARNINGS_CXXFLAGS} -Werror=sequence-point"
-    _WARNINGS_CXXFLAGS="${_WARNINGS_CXXFLAGS} -Werror=switch"
     _WARNINGS_CXXFLAGS="${_WARNINGS_CXXFLAGS} -Werror=unused-label"
     _WARNINGS_CXXFLAGS="${_WARNINGS_CXXFLAGS} -Werror=trigraphs"
     _WARNINGS_CXXFLAGS="${_WARNINGS_CXXFLAGS} -Werror=type-limits"