[Backtracing] Fix a couple of Linux specific issues.

Linux gives the main thread a name based on the process name, and also
we need to tolerate an extra slash on the `<compiler-generated>` filename
for some reason.

rdar://121430255

Author: al45tair

stdlib/public/libexec/swift-backtrace/main.swift

@@ -606,8 +606,8 @@ Generate a backtrace for the parent process.
           while fd < 0 && (errno == EEXIST || errno == EINTR) {
             if errno != EINTR {
               ndx += 1
+              filename = "\(args.outputPath)/\(name)-\(pid)-\(now.tv_sec).\(now.tv_nsec)-\(ndx).\(ext)"
             }
-            filename = "\(args.outputPath)/\(name)-\(pid)-\(now.tv_sec).\(now.tv_nsec)-\(ndx).\(ext)"
             fd = open(filename, O_RDWR|O_CREAT|O_EXCL, 0o644)
           }
 

test/Backtracing/JSON.swift

@@ -85,7 +85,10 @@ struct Crash {
 
 // CHECK-NEXT: "threads": [
 // CHECK-NEXT:   {
-// CHECK-NEXT:     "crashed": true,
+
+// On Linux there's a name here
+
+// CHECK:          "crashed": true,
 // CHECK-NEXT:     "registers": {
 // CHECK-NEXT:       "{{.*}}": "0x{{[0-9a-f]+}}",
 
@@ -180,7 +183,7 @@ struct Crash {
 // CHECK-NEXT:         "description": "static Crash.$main() + [[OFFSET]]",
 // CHECK-NEXT:         "image": "Crash",
 // CHECK-NEXT:         "sourceLocation": {
-// CHECK-NEXT:           "file": "{{/?}}<compiler-generated>",
+// CHECK-NEXT:           "file": "{{/*}}<compiler-generated>",
 // CHECK-NEXT:           "line": 0,
 // CHECK-NEXT:           "column": 0
 // CHECK-NEXT:         }
@@ -218,8 +221,8 @@ struct Crash {
 // Maybe multiple images before this one
 
 // CHECK:          "name": "Crash",
-// CHECK-NEXT:     "buildId": "{{([0-9a-f][0-9a-f])+}}",
-// CHECK-NEXT:     "path": "{{.*}}/Crash",
+//                 "buildId": ... is optional
+// CHECK:          "path": "{{.*}}/Crash",
 // CHECK-NEXT:     "baseAddress": "0x{{[0-9a-f]+}}",
 // CHECK-NEXT:     "endOfText": "0x{{[0-9a-f]+}}"
 // CHECK-NEXT:   }

test/Backtracing/JSONAsync.swift

@@ -166,7 +166,7 @@ struct JSONAsync {
 // CHECK-NEXT:         "offset": [[OFFSET:[0-9]+]],
 // CHECK-NEXT:         "image": "JSONAsync",
 // CHECK-NEXT:         "sourceLocation": {
-// CHECK-NEXT:           "file": "{{/?}}<compiler-generated>",
+// CHECK-NEXT:           "file": "{{/*}}<compiler-generated>",
 // CHECK-NEXT:           "line": 0,
 // CHECK-NEXT:           "column": 0
 // CHECK-NEXT:         }
@@ -179,7 +179,7 @@ struct JSONAsync {
 // CHECK-NEXT:         "offset": [[OFFSET:[0-9]+]],
 // CHECK-NEXT:         "image": "JSONAsync",
 // CHECK-NEXT:         "sourceLocation": {
-// CHECK-NEXT:           "file": "{{/?}}<compiler-generated>",
+// CHECK-NEXT:           "file": "{{/*}}<compiler-generated>",
 // CHECK-NEXT:           "line": 0,
 // CHECK-NEXT:           "column": 0
 // CHECK-NEXT:         }
@@ -206,8 +206,8 @@ struct JSONAsync {
 // Maybe multiple images before this one
 
 // CHECK:          "name": "JSONAsync",
-// CHECK-NEXT:     "buildId": "{{([0-9a-f][0-9a-f])+}}",
-// CHECK-NEXT:     "path": "{{.*}}/JSONAsync",
+//                 "buildId": ... is optional
+// CHECK:          "path": "{{.*}}/JSONAsync",
 // CHECK-NEXT:     "baseAddress": "0x{{[0-9a-f]+}}",
 // CHECK-NEXT:     "endOfText": "0x{{[0-9a-f]+}}"
 // CHECK-NEXT:   }