[spirv-writer] Simple if statements.

This CL adds the code to generate simple if statements.

Bug: tint:5
Change-Id: Ied42ad8b3632d7926ac646d1aa21e190a7a2c07e
Reviewed-on: https://dawn-review.googlesource.com/c/tint/+/19411
Reviewed-by: David Neto <dneto@google.com>
diff --git a/src/CMakeLists.txt b/src/CMakeLists.txt
index 83cee3e..609542c 100644
--- a/src/CMakeLists.txt
+++ b/src/CMakeLists.txt
@@ -427,6 +427,7 @@
     writer/spirv/builder_function_variable_test.cc
     writer/spirv/builder_global_variable_test.cc
     writer/spirv/builder_ident_expression_test.cc
+    writer/spirv/builder_if_test.cc
     writer/spirv/builder_literal_test.cc
     writer/spirv/builder_return_test.cc
     writer/spirv/builder_test.cc