Add function sections test

Author: asuhan

test/LinkerSections/Inputs/FunctionSections.swift

@@ -0,0 +1,5 @@
+public typealias Void = ()
+
+public func func1() -> Void {}
+
+public func func2() -> Void {}

test/LinkerSections/Inputs/FunctionSectionsUse.swift

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+import FunctionSections
+
+func1()

test/LinkerSections/function_sections.swift

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+// REQUIRES: OS=linux-gnu || OS=linux-androideabi || OS=linux-android || OS=freebsd
+// RUN: %empty-directory(%t)
+// RUN: %target-build-swift -Xfrontend -function-sections -emit-module -emit-library -static -parse-stdlib %S/Inputs/FunctionSections.swift
+// RUN: %target-build-swift -Xlinker --gc-sections -Xlinker -Map=%t/../../FunctionSections.map -I%t/../.. -L%t/../.. -lFunctionSections %S/Inputs/FunctionSectionsUse.swift
+// RUN: %FileCheck %s < %t/../../FunctionSections.map
+
+// CHECK: Discarded input sections
+// CHECK: .text.$s16FunctionSections5func2yyF
+// CHECK: Memory map
+// CHECK: .text.$s16FunctionSections5func1yyF

test/LinkerSections/function_sections_ir_check.swift

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+// RUN: %empty-directory(%t)
+// RUN: %target-build-swift -Xfrontend -function-sections -emit-library -emit-ir -static -parse-stdlib %S/Inputs/FunctionSections.swift | %FileCheck %s
+
+// CHECK: define {{(dllexport |protected )?}}swiftcc void @"$s16FunctionSections5func1yyF"() #0 {
+// CHECK: entry:
+// CHECK:   ret void
+// CHECK: }
+
+// CHECK: define {{(dllexport |protected )?}}swiftcc void @"$s16FunctionSections5func2yyF"() #0 {
+// CHECK: entry:
+// CHECK:   ret void
+// CHECK: }