[WebAssembly] Define __heap_base global

This is an immutable exported global representing
the start of the heap area.  It is a page aligned.

Differential Revision: https://reviews.llvm.org/D42030

llvm-svn: 322609
diff --git a/lld/test/wasm/data-layout.ll b/lld/test/wasm/data-layout.ll
index a32e788..1fdec48 100644
--- a/lld/test/wasm/data-layout.ll
+++ b/lld/test/wasm/data-layout.ll
@@ -22,30 +22,36 @@
 ; CHECK-NEXT:         Mutable:         false
 ; CHECK-NEXT:         InitExpr:
 ; CHECK-NEXT:           Opcode:          I32_CONST
-; CHECK-NEXT:           Value:           1024
+; CHECK-NEXT:           Value:           66608
 ; CHECK-NEXT:       - Index:           2
 ; CHECK-NEXT:         Type:            I32
 ; CHECK-NEXT:         Mutable:         false
 ; CHECK-NEXT:         InitExpr:
 ; CHECK-NEXT:           Opcode:          I32_CONST
-; CHECK-NEXT:           Value:           1040
+; CHECK-NEXT:           Value:           1024
 ; CHECK-NEXT:       - Index:           3
 ; CHECK-NEXT:         Type:            I32
 ; CHECK-NEXT:         Mutable:         false
 ; CHECK-NEXT:         InitExpr:
 ; CHECK-NEXT:           Opcode:          I32_CONST
-; CHECK-NEXT:           Value:           1048
+; CHECK-NEXT:           Value:           1040
 ; CHECK-NEXT:       - Index:           4
 ; CHECK-NEXT:         Type:            I32
 ; CHECK-NEXT:         Mutable:         false
 ; CHECK-NEXT:         InitExpr:
 ; CHECK-NEXT:           Opcode:          I32_CONST
+; CHECK-NEXT:           Value:           1048
+; CHECK-NEXT:       - Index:           5
+; CHECK-NEXT:         Type:            I32
+; CHECK-NEXT:         Mutable:         false
+; CHECK-NEXT:         InitExpr:
+; CHECK-NEXT:           Opcode:          I32_CONST
 ; CHECK-NEXT:           Value:           1052
 
 ; CHECK:       - Type:            DATA
 ; CHECK-NEXT:     Relocations:
 ; CHECK-NEXT:       - Type:            R_WEBASSEMBLY_MEMORY_ADDR_I32
-; CHECK-NEXT:         Index:           4
+; CHECK-NEXT:         Index:           5
 ; CHECK-NEXT:         Offset:          0x0000001F
 ; CHECK-NEXT:     Segments:
 ; CHECK-NEXT:       - SectionOffset:   7