Workaround for:

https://bugzilla.mozilla.org/show_bug.cgi?id=1450912

GCC libstdc++ should be fixed to support locales on Solaris so that
std::regex functionality works.

diff --git a/comm/mail/app/nsMailApp.cpp b/comm/mail/app/nsMailApp.cpp
index b16b25a..cb84b69 100644
--- a/comm/mail/app/nsMailApp.cpp
+++ b/comm/mail/app/nsMailApp.cpp
@@ -246,6 +246,10 @@ uint32_t gBlocklistInitFlags = eDllBlocklistInitFlagDefault;
 #endif
 
 int main(int argc, char* argv[], char* envp[]) {
+
+  // Workaround for https://bugzilla.mozilla.org/show_bug.cgi?id=1450912
+  setenv("LC_ALL", "C", 1);
+
 #if defined(MOZ_ENABLE_FORKSERVER)
   if (strcmp(argv[argc - 1], "forkserver") == 0) {
     nsresult rv = InitXPCOMGlue(LibLoadingStrategy::NoReadAhead);