[Test] Fix function_sections test to support different linkers.

`gold` and `lld` produce map files in different formats; this test
can and should work for both of them.

rdar://123504095

Author: al45tair

test/LinkerSections/function_sections.swift

@@ -1,10 +1,13 @@
 // REQUIRES: OS=linux-gnu || 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
+// RUN: %target-build-swift -Xlinker -v -Xlinker --gc-sections -Xlinker -Map=%t/../../FunctionSections.map -I%t/../.. -L%t/../.. -lFunctionSections %S/Inputs/FunctionSectionsUse.swift 2>&1 | sed 's/.*\(gold\|LLD\).*/\1/g' | tr "[:lower:]" "[:upper:]" > %t/../../Linker.txt
+// RUN: %FileCheck --check-prefix $(cat %t/../../Linker.txt) %s < %t/../../FunctionSections.map
 
-// CHECK: Discarded input sections
-// CHECK: .text.$s16FunctionSections5func2yyF
-// CHECK: Memory map
-// CHECK: .text.$s16FunctionSections5func1yyF
+// GOLD: Discarded input sections
+// GOLD: .text.$s16FunctionSections5func2yyF
+// GOLD: Memory map
+// GOLD: .text.$s16FunctionSections5func1yyF
+
+// LLD: .text.$s16FunctionSections5func1yyF
+// LLD-NOT: .text.$s16FunctionSections5func2yyF