Issue #1699 - Part 3c: mozjemalloc: FreeBSD: Ensure early initialization

This guarantees that initialization is done in a single-thread context.

build/gecko_templates.mozbuild

@@ -63,6 +63,11 @@ def GeckoBinary(linkage='dependent', msvcrt='dynamic', mozglue=None):
                     LDFLAGS += ['-rdynamic']
                 if CONFIG['MOZ_MEMORY']:
                     USE_LIBS += ['memory']
+                    if CONFIG['OS_ARCH'] == 'FreeBSD':
+                        # Make sure this function is linked in, so that it is
+                        # executed at executable load (it has the 'constructor'
+                        # flag).
+                        LDFLAGS += ['-u', 'jemalloc_FreeBSD_init']
         elif mozglue == 'library':
             LIBRARY_DEFINES['MOZ_HAS_MOZGLUE'] = True
             if not CONFIG['MOZ_GLUE_IN_PROGRAM']: