Make it possible to run dotest on Linux without any parameters

[vharron]

Summary

dotest will select clang-3.5 by default and fall back on clang/gcc
dotest will look for the lldb executable in the typical cmake
output locations:
{lldb}/../../../build/bin (next to llvm directory)
{lldb}/../../../build/host/bin (next to llvm directory)
{lldb}/../build/bin (next to lldb directory)
{lldb}/../build/host/bin (next to lldb directory)

[clayborg]

lgtm

[vharron]

r237632

test/dotest.py

def parseOptionsAndInitTestdirs():
 
     if args.compilers:
         compilers = args.compilers
     else:
         # Use a compiler appropriate appropriate for the Apple SDK if one was specified
         if platform_system == 'Darwin' and args.apple_sdk:
             compilers = [commands.getoutput('xcrun -sdk "%s" -find clang 2> /dev/null' % (args.apple_sdk))]
         else:
-            compilers = ['clang']
+            # 'clang' on ubuntu 14.04 is 3.4 so we try clang-3.5 first
+            candidateCompilers = ['clang-3.5', 'clang', 'gcc']
+            for candidate in candidateCompilers:
+                if which(candidate):
+                    compilers = [candidate]
+                    break
 
     if args.channels:
         lldbtest_config.channels = args.channels
 
     if args.log_success:
         lldbtest_config.log_success = args.log_success
 
     # Set SDKROOT if we are using an Apple SDK
def getOutputPaths(lldbRootDirectory):
     """
     Returns typical build output paths for the lldb executable
 
     lldbDirectory - path to the root of the lldb svn/git repo
     """
     result = []
 
     if sys.platform == 'darwin':
-        result.extend(getXcodeOutputPaths(lldbRootDirectory))
+        result.append(getXcodeOutputPaths(lldbRootDirectory))
 
     # cmake builds?  look for build or build/host folder next to llvm directory
-    # lldb is located in llvm/tools/lldb
+    # lldb is located in llvm/tools/lldb so we need to go up three levels
     llvmParentDir = os.path.abspath(os.path.join(lldbRootDirectory, os.pardir, os.pardir, os.pardir))
-    result.extend(os.path.join(llvmParentDir, 'build', 'bin'))
-    result.extend(os.path.join(llvmParentDir, 'build', 'host', 'bin'))
+    result.append(os.path.join(llvmParentDir, 'build', 'bin'))
+    result.append(os.path.join(llvmParentDir, 'build', 'host', 'bin'))
+
+    # some cmake developers keep their build directory beside their lldb directory
+    lldbParentDir = os.path.abspath(os.path.join(lldbRootDirectory, os.pardir))
+    result.append(os.path.join(lldbParentDir, 'build', 'bin'))
+    result.append(os.path.join(lldbParentDir, 'build', 'host', 'bin'))
 
     return result
 
 def setupSysPath():
     """
     Add LLDB.framework/Resources/Python to the search paths for modules.
     As a side effect, we also discover the 'lldb' executable and export it here.
     """