Issue #2079 - Fix linking libxul on *nix when using a linker other than bfd.

Don't mark the .kPStaticModules section as relro for bfd, as the linkers on
 Windows and Mac don't do this anyway.
Add a section insert of .kPStaticModules to config/expandlibs_exec.py, which
 seems to be the primary cause of linking bustage on gold, lld, and mold.

config/expandlibs_exec.py

@@ -45,6 +45,7 @@ SECTION_INSERT_BEFORE = [
   ('.text', '.fini'),
   ('.rodata', '.rodata1'),
   ('.data.rel.ro', '.dynamic'),
+  ('.kPStaticModules', '.data.rel.ro'),
   ('.data', '.data1'),
 ]
 

toolkit/library/StaticXULComponents.ld

@@ -1,5 +0,0 @@
-SECTIONS {
-  .data.rel.ro : {
-    *(.kPStaticModules)
-  }
-}

toolkit/library/libxul.mk

@@ -39,21 +39,6 @@ ifeq ($(OS_ARCH),SunOS)
 OS_LDFLAGS += -Wl,-z,defs
 endif
 
-# BFD ld doesn't create multiple PT_LOADs as usual when an unknown section
-# exists. Using an implicit linker script to make it fold that section in
-# .data.rel.ro makes it create multiple PT_LOADs. That implicit linker
-# script however makes gold misbehave, first because it doesn't like that
-# the linker script is given after crtbegin.o, and even past that, replaces
-# the default section rules with those from the script instead of
-# supplementing them. Which leads to a lib with a huge load of sections.
-ifneq (OpenBSD,$(OS_TARGET))
-ifneq (WINNT,$(OS_TARGET))
-ifdef LD_IS_BFD
-OS_LDFLAGS += $(topsrcdir)/toolkit/library/StaticXULComponents.ld
-endif
-endif
-endif
-
 ifdef _MSC_VER
 get_first_and_last = dumpbin -exports $1 | grep _NSModule@@ | sort -k 3 | sed -n 's/^.*?\([^@]*\)@@.*$$/\1/;1p;$$p'
 else