Fill in source locations in implicit function builder expressions

to satisfy the code-coverage instrumentation.

rdar://51612977

test/Profiler/coverage_function_builder.swift

@@ -0,0 +1,31 @@
+// RUN: %target-swift-frontend -Xllvm -sil-full-demangle -profile-generate -profile-coverage-mapping -emit-sorted-sil -emit-sil -module-name coverage_functon_builder %s | %FileCheck %s
+
+@_functionBuilder
+struct Summer {
+  static func buildBlock(_ x: Int...) -> Int {
+    return x.reduce(0, +)
+  }
+  static func buildIf(_ x: Int?) -> Int {
+    return x ?? 0
+  }
+}
+
+// CHECK-LABEL: sil_coverage_map {{.*}} "$s24coverage_functon_builder5test0SiyF"
+@Summer
+func test0() -> Int {
+  // CHECK: [[@LINE-1]]:21 -> [[@LINE+3]]:2 : 0
+  18
+  12
+}
+
+// CHECK-LABEL: sil_coverage_map {{.*}} "$s24coverage_functon_builder5test1SiyF"
+@Summer
+func test1() -> Int {
+  // CHECK: [[@LINE-1]]:21 -> [[@LINE+7]]:2 : 0
+  18
+  12
+  if 7 < 23 {
+    11
+    8
+  }
+}