Change AsyncProcess stdout/err reads to 4096 instead of Int.max

- this should allow us to consume available in the Pipe as its
  filled and flushed but the running process.

rdar://155634107

Author: daveinglis

Sources/Basics/Concurrency/AsyncProcess.swift

@@ -517,7 +517,8 @@ package final class AsyncProcess {
 
             group.enter()
             stdoutPipe.fileHandleForReading.readabilityHandler = { (fh: FileHandle) in
-                let data = (try? fh.read(upToCount: Int.max)) ?? Data()
+                // 4096 is default pipe buffer size so reading in that size seems most efficient and still get output as it available
+                let data = (try? fh.read(upToCount: 4096)) ?? Data()
                 if data.count == 0 {
                     stdoutPipe.fileHandleForReading.readabilityHandler = nil
                     group.leave()
@@ -532,7 +533,8 @@ package final class AsyncProcess {
 
             group.enter()
             stderrPipe.fileHandleForReading.readabilityHandler = { (fh: FileHandle) in
-                let data = (try? fh.read(upToCount: Int.max)) ?? Data()
+                // 4096 is default pipe buffer size so reading in that size seems most efficient and still get output as it available
+                let data = (try? fh.read(upToCount: 4096)) ?? Data()
                 if data.count == 0 {
                     stderrPipe.fileHandleForReading.readabilityHandler = nil
                     group.leave()