Fix ToolsetVer regex

Author: 0181532686cf4a31163be0bf3e6bb6732bf

cmake/GetBoostLibB2Args.cmake

@@ -71,7 +71,7 @@ function(get_boots_lib_b2_args)
         else()
             list(APPEND b2Args cxxflags=-fPIC cxxflags=-std=c++11)
             # Need to configure the toolset based on whatever version CMAKE_CXX_COMPILER is
-            string(REGEX MATCH "[0-9]+\\.[0-9]+\\.[0-9]" ToolsetVer "${CMAKE_CXX_COMPILER_VERSION}")
+            string(REGEX MATCH "[0-9]+\\.[0-9]+(?:\\.[0-9]+)?" ToolsetVer "${CMAKE_CXX_COMPILER_VERSION}")
             if(CMAKE_CXX_COMPILER_ID MATCHES "^(Apple)?Clang$")
                 list(APPEND b2Args toolset=clang-${ToolsetVer})
                 if(HAVE_LIBC++)
@@ -84,4 +84,4 @@ function(get_boots_lib_b2_args)
     endif()
 
     set(b2Args "${b2Args}" PARENT_SCOPE)
-endfunction(get_boots_lib_b2_args)
+endfunction(get_boots_lib_b2_args)