config fail with multiple VS installed

```
zhaoqin@ZHAOQIN4-W ~/Workspace/DynamoRIO/builds/build_x64_dbg.git
$ rm * -fr

zhaoqin@ZHAOQIN4-W ~/Workspace/DynamoRIO/builds/build_x64_dbg.git
$ ninja_x64

zhaoqin@ZHAOQIN4-W ~/Workspace/DynamoRIO/builds/build_x64_dbg.git
$ compilerVS2010_64

zhaoqin@ZHAOQIN4-W ~/Workspace/DynamoRIO/builds/build_x64_dbg.git
$ cmake -DDEBUG=ON -DBUILD_TESTS=ON ../../dynamorio.git/
-- Building for: Visual Studio 11 2012
-- The C compiler identification is MSVC 17.0.61030.0
-- Check for working C compiler using: Visual Studio 11 2012
-- Check for working C compiler using: Visual Studio 11 2012 -- works
-- Detecting C compiler ABI info
-- Detecting C compiler ABI info - done
-- The CXX compiler identification is MSVC 17.0.61030.0
-- Check for working CXX compiler using: Visual Studio 11 2012
-- Check for working CXX compiler using: Visual Studio 11 2012 -- works
-- Detecting CXX compiler ABI info
-- Detecting CXX compiler ABI info - done
-- Detecting CXX compile features
-- Detecting CXX compile features - done
-- Version number: 5.0.16709
-- Found assembler: C:/Program Files (x86)/Microsoft Visual Studio 10.0/VC/bin/ml.exe
-- Found message compiler: C:/Program Files (x86)/Microsoft SDKs/Windows/v7.0A/Bin/MC.Exe
-- Found Perl: D:/src/cygwin/bin/perl.exe (found version "5.14.2")
-- Targeting subsystem 5.01
CMake Error at CMakeLists.txt:1175 (message):
*** C:/Program Files (x86)/Microsoft Visual Studio 11.0/VC/bin/cl.exe
failed: ***

-- Configuring incomplete, errors occurred!
See also "D:/src/cygwin/home/zhaoqin/Workspace/DynamoRIO/builds/build_x64_dbg.git/CMakeFiles/CMakeOutput.log".
```

It looks like CMake find VS2012's cl.exe and link.exe but VS2010's ml.exe

```
//path to assembler
CMAKE_ASM_COMPILER:FILEPATH=C:/Program Files (x86)/Microsoft Visual Studio 10.0/VC/bin/ml.exe

//Path to a program.
CMAKE_LINKER:FILEPATH=C:/Program Files (x86)/Microsoft Visual Studio 11.0/VC/bin/link.exe
```