Emit coverage mappings for all modules

Previously in WMO builds where IR was multithreaded only the
primary module would emit the coverage mapping leading to only the first
object file to have the __llvm_covmap section. This change emits
coverage for all modules so they are correctly reflected in the final
coverage report.

Author: keith

lib/IRGen/GenDecl.cpp

@@ -1105,8 +1105,11 @@ void IRGenerator::emitGlobalTopLevel(llvm::StringSet<> *linkerDirectives) {
     IGM->emitSILDifferentiabilityWitness(&dw);
   }
 
-  // Emit code coverage mapping data.
-  PrimaryIGM->emitCoverageMapping();
+  // Emit code coverage mapping data for all modules
+  for (auto Iter : *this) {
+    IRGenModule *IGM = Iter.second;
+    IGM->emitCoverageMapping();
+  }
 
   for (auto Iter : *this) {
     IRGenModule *IGM = Iter.second;

test/Profiler/Inputs/coverage_num_threads1.swift

@@ -0,0 +1 @@
+func func1() {}

test/Profiler/Inputs/coverage_num_threads2.swift

@@ -0,0 +1 @@
+func func2() {}

test/Profiler/coverage_num_threads.swift

@@ -0,0 +1,12 @@
+// RUN: %target-swift-frontend -profile-generate -profile-coverage-mapping -num-threads 0 -emit-ir %S/Inputs/coverage_num_threads1.swift | %FileCheck %s -check-prefix=SINGLE-SOURCE --implicit-check-not="llvm_coverage_mapping ="
+
+// SINGLE-SOURCE: llvm_coverage_mapping =
+
+// RUN: %target-swift-frontend -profile-generate -profile-coverage-mapping -num-threads 0 -emit-ir %S/Inputs/coverage_num_threads1.swift %S/Inputs/coverage_num_threads2.swift | %FileCheck %s -check-prefix=SINGLE-OBJECT --implicit-check-not="llvm_coverage_mapping ="
+
+// SINGLE-OBJECT: llvm_coverage_mapping =
+
+// RUN: %target-swift-frontend -profile-generate -profile-coverage-mapping -num-threads 2 -emit-ir %S/Inputs/coverage_num_threads1.swift %S/Inputs/coverage_num_threads2.swift | %FileCheck %s -check-prefix=MULTIPLE-OBJECTS --implicit-check-not="llvm_coverage_mapping ="
+
+// MULTIPLE-OBJECTS: llvm_coverage_mapping =
+// MULTIPLE-OBJECTS: llvm_coverage_mapping =