[PATCH] BaseTools: Enable MAX_CONCURRENT_THREAD_NUMBER = 0 feature

["Feng, YunhuaX" <yunhuax.feng@intel.com>]

Adding 'MAX_CONCURRENT_THREAD_NUMBER=0' option for user to
enable 'auto-detect thread number' feature, and changing default value 
to '0' when initial build environment is configured.

Fixes: https://bugzilla.tianocore.org/show_bug.cgi?id=775
Cc: Liming Gao <liming.gao@intel.com>
Cc: Yonghong Zhu <yonghong.zhu@intel.com>
Contributed-under: TianoCore Contribution Agreement 1.1
Signed-off-by: Yunhua Feng <yunhuax.feng@intel.com>
---
 BaseTools/Conf/target.template         | 5 +++--
 BaseTools/Source/Python/build/build.py | 6 +++++-
 2 files changed, 8 insertions(+), 3 deletions(-)

diff --git BaseTools/Conf/target.template BaseTools/Conf/target.template
index 787fc64fb1..ee8745610f 100644
--- BaseTools/Conf/target.template
+++ BaseTools/Conf/target.template
@@ -61,8 +61,9 @@ TOOL_CHAIN_TAG        = MYTOOLS
 
 # MAX_CONCURRENT_THREAD_NUMBER  NUMBER  Optional  The number of concurrent threads. Recommend to set this
 #                                                 value to one more than the number of your compurter
-#                                                 cores or CPUs. Less than 2 means disable multithread build.
-MAX_CONCURRENT_THREAD_NUMBER = 1
+#                                                 cores or CPUs. automatically detect number of processor threads
+#                                                 when 'MAX_CONCURRENT_THREAD_NUMBER=0'
+MAX_CONCURRENT_THREAD_NUMBER = 0
 
 
 # BUILD_RULE_CONF  Filename Optional  Specify the file name to use for the build rules that are followed
diff --git BaseTools/Source/Python/build/build.py BaseTools/Source/Python/build/build.py
index 38498046d7..fd2681e05d 100644
--- BaseTools/Source/Python/build/build.py
+++ BaseTools/Source/Python/build/build.py
@@ -26,6 +26,7 @@ import platform
 import traceback
 import encodings.ascii
 import itertools
+import multiprocessing
 
 from struct import *
 from threading import *
@@ -936,7 +937,10 @@ class Build():
                 self.ThreadNumber = int(self.ThreadNumber, 0)
 
         if self.ThreadNumber == 0:
-            self.ThreadNumber = 1
+            try:
+                self.ThreadNumber = multiprocessing.cpu_count()
+            except (ImportError, NotImplementedError):
+                self.ThreadNumber = 1
 
         if not self.PlatformFile:
             PlatformFile = self.TargetTxt.TargetTxtDictionary[DataType.TAB_TAT_DEFINES_ACTIVE_PLATFORM]
-- 
2.12.2.windows.2