[FIX] mozilla ComputeRandomAllocationAddress

Similar to devel/spidermonkey60 change. Allow OpenBSD's mmap to
handle ASLR by using NULL as hint to mmap.

Built and lightly tested on amd64 (although not exactly sure
how to ensure java script is executed in thunderbird).

okay?

Did I miss any copies of mozilla java script in other ports?

Index: mail/mozilla-thunderbird/Makefile
===================================================================
RCS file: /cvs/ports/mail/mozilla-thunderbird/Makefile,v
retrieving revision 1.296
diff -u -p -u -r1.296 Makefile
--- mail/mozilla-thunderbird/Makefile 22 Sep 2019 17:19:07 -0000 1.296
+++ mail/mozilla-thunderbird/Makefile 30 Sep 2019 18:21:54 -0000
@@ -10,6 +10,7 @@ MOZILLA_VERSION = 68.1.0
MOZILLA_BRANCH = release
MOZILLA_PROJECT = thunderbird
MOZILLA_CODENAME = comm/mail
+REVISION = 0
EXTRACT_SUFX = .tar.xz

MULTI_PACKAGES = -main -lightning
Index: mail/mozilla-thunderbird/patches/patch-js_src_jit_ProcessExecutableMemory_cpp
===================================================================
RCS file: mail/mozilla-thunderbird/patches/patch-js_src_jit_ProcessExecutableMemory_cpp
diff -N mail/mozilla-thunderbird/patches/patch-js_src_jit_ProcessExecutableMemory_cpp
--- /dev/null 1 Jan 1970 00:00:00 -0000
+++ mail/mozilla-thunderbird/patches/patch-js_src_jit_ProcessExecutableMemory_cpp 30 Sep 2019 18:21:54 -0000
@@ -0,0 +1,26 @@
+$OpenBSD$
+
+Index: js/src/jit/ProcessExecutableMemory.cpp
+--- js/src/jit/ProcessExecutableMemory.cpp.orig
++++ js/src/jit/ProcessExecutableMemory.cpp
+@@ -318,6 +318,12 @@ static void DecommitPages(void* addr, size_t bytes) {
+ }
+ #else // !XP_WIN
+ static void* ComputeRandomAllocationAddress() {
++#ifdef __OpenBSD__
++ // OpenBSD already has random mmap and the idea that all x64 cpus
++ // have 48-bit address space is not correct. Returning nullptr
++ // allows OpenBSD do to the right thing.
++ return nullptr;
++#else
+ uint64_t rand = js::GenerateRandomSeed();
+
+ # ifdef HAVE_64BIT_BUILD
+@@ -337,6 +343,7 @@ static void* ComputeRandomAllocationAddress() {
+ // Ensure page alignment.
+ uintptr_t mask = ~uintptr_t(gc::SystemPageSize() - 1);
+ return (void*)uintptr_t(rand & mask);
++