[WebAssembly] Assembler: recognize .init_array as data section.

[sbc100]

Can we get a test for this?

[aardappel]

Added test.

lib/MC/MCParser/WasmAsmParser.cpp

if (Lexer->isNot(AsmToken::String))
       return error("expected string in directive, instead got: ", Lexer->getTok());
 
     auto Kind = StringSwitch<Optional<SectionKind>>(Name)
                     .StartsWith(".data", SectionKind::getData())
                     .StartsWith(".rodata", SectionKind::getReadOnly())
                     .StartsWith(".text", SectionKind::getText())
                     .StartsWith(".custom_section", SectionKind::getMetadata())
                     .StartsWith(".bss", SectionKind::getBSS())
+                    // See use of .init_array in WasmObjectWriter and
+                    // TargetLoweringObjectFileWasm
+                    .StartsWith(".init_array", SectionKind::getData())
                     .Default(Optional<SectionKind>());
     if (!Kind.hasValue())
       return Parser->Error(Lexer->getLoc(), "unknown section kind: " + Name);
 
     MCSectionWasm *Section = getContext().getWasmSection(Name, Kind.getValue());
 
     // Update section flags if present in this .section directive
     bool Passive = false;

test/MC/WebAssembly/basic-assembly.s

 .L.str:
     .int8       'H'
     .asciz      "ello, World!"
     .int16      1234
     .int64      5000000000
     .int32      2000000000
     .size       .L.str, 28
 
+    .section    .init_array.42,"",@
+    .p2align    2
+    .int32      test0
+
     .ident      "clang version 9.0.0 (trunk 364502) (llvm/trunk 364571)"
     .globaltype __stack_pointer, i32
 
 # CHECK:           .text
 # CHECK-LABEL: test0:
 # CHECK-NEXT:      .functype   test0 (i32, i64) -> (i32)
 # CHECK-NEXT:      .eventtype  __cpp_exception i32
 # CHECK-NEXT:      .local      f32, f64

 # CHECK-NEXT:      global.get  __stack_pointer
 # CHECK-NEXT:      end_function
 
 # CHECK:           .section    .rodata..L.str,"",@
 # CHECK-NEXT:      .hidden     .L.str
 # CHECK-NEXT:  .L.str:
 # CHECK-NEXT:      .int8       72
 # CHECK-NEXT:      .asciz      "ello, World!"
-# CHECK-NEXT:      .int16       1234
-# CHECK-NEXT:      .int64       5000000000
-# CHECK-NEXT:      .int32       2000000000
+# CHECK-NEXT:      .int16      1234
+# CHECK-NEXT:      .int64      5000000000
+# CHECK-NEXT:      .int32      2000000000
+# CHECK-NEXT:      .size       .L.str, 28
+
+# CHECK:           .section    .init_array.42,"",@
+# CHECK-NEXT:      .p2align    2
+# CHECK-NEXT:      .int32      test0
 
 # CHECK:           .globaltype __stack_pointer, i32