PNaCl: Fix negative relocation addends on x86-32

test/NaCl/X86/negative-addend.ll

+; RUN: pnacl-llc -mtriple=i386-unknown-nacl -filetype=obj %s -o - \
+; RUN:   | llvm-objdump -r - | FileCheck %s -check-prefix=X8632
+; RUN: pnacl-llc -mtriple=x86_64-unknown-nacl -filetype=obj %s -o - \
+; RUN:   | llvm-objdump -r - | FileCheck %s -check-prefix=X8664
+
+; Check that "add" works for negative values when used as a
+; ConstantExpr in a global variable initializer.
+; See: https://code.google.com/p/nativeclient/issues/detail?id=3548
+
+
+; @spacer and @var end up in the BSS section.
+; @spacer is at offset 0.  @var is at offset 4096 = 0x1000.
+
+@spacer = internal global [4096 x i8] zeroinitializer
+@var = internal global i32 zeroinitializer
+
+@negative_offset = internal global i32 add
+    (i32 ptrtoint (i32* @var to i32), i32 -8)
+
+; Note that the addend 4294971384 below equals 0x100000ff8, where
+; 0xff8 comes from subtracting 8 from the offset of @var.
+
+; X8632: RELOCATION RECORDS FOR [.data]:
+; X8632-NEXT: 0 R_386_32 Unknown
+
+; X8664: RELOCATION RECORDS FOR [.data]:
+; X8664-NEXT: 0 R_X86_64_32 .bss+4294971384