Fix Klocwork non null terminated string with default C++11 ABI

After switching libstdc++ from the old to the default, new C++11 ABI,
Klocwork static analysis flags that assignment to std::string with a
string literal may result in a non null terminated string. While it is
not apparent whether this is a false-positive or not, initializing the
string with the literal by default resolves the Klocwork issue.

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182 (Local) /__w/fpga-runtime-for-opencl/fpga-runtime-for-opencl/src/acl_hal_mmd.cpp:782 NNTS.MUST (1:Critical) Analyze
Buffer overflow of 'board_vendor_path._M_dataplus._M_p' due to non null terminated string 'board_vendor_path._M_dataplus._M_p'
  * acl_hal_mmd.cpp:773: customer_board_vendor_path is false
  * acl_hal_mmd.cpp:779: 'board_vendor_path._M_dataplus._M_p' may not be null-terminated after calling 'operator='.
    * basic_string.h:705: 'this->_M_dataplus._M_p' may not be null-terminated after calling 'assign'.
      * basic_string.h:1438: 'this->_M_dataplus._M_p' may not be null-terminated after calling '_M_replace'.
        * basic_string.tcc:429: __new_size<=this->capacity() is false
        * basic_string.tcc:465: 'this->_M_dataplus._M_p' may not be null-terminated after calling '_M_mutate'.
          * basic_string.tcc:318: __pos is true
          * basic_string.tcc:319: '__r' may not be null-terminated after calling '_S_copy'.
            * basic_string.h:348: __n==1 is false
            * basic_string.h:351: '__d' may not be null-terminated after calling 'copy'.
              * char_traits.h:365: The size parameter may be less than length of source buffer.
              * char_traits.h:365: '__s1' may not be null-terminated after calling '__builtin_memcpy'.
          * basic_string.tcc:320: __len2 is false
          * basic_string.tcc:320: __s&&__len2 is false
          * basic_string.tcc:322: __how_much is false
          * basic_string.tcc:327: _M_data(__r): copies '__r' into 'this->_M_dataplus._M_p'
  * acl_hal_mmd.cpp:783: board_vendor_path.c_str(): returns 'board_vendor_path._M_dataplus._M_p'
  * acl_hal_mmd.cpp:782: String 'board_vendor_path._M_dataplus._M_p' is not properly terminated and is passed as an argument to function 'printf'.
Current status 'Analyze'

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183 (Local) /__w/fpga-runtime-for-opencl/fpga-runtime-for-opencl/src/acl_hal_mmd.cpp:798 NNTS.MUST (1:Critical) Analyze
Buffer overflow of 'board_vendor_path._M_dataplus._M_p' due to non null terminated string 'board_vendor_path._M_dataplus._M_p'
  * acl_hal_mmd.cpp:773: customer_board_vendor_path is false
  * acl_hal_mmd.cpp:779: 'board_vendor_path._M_dataplus._M_p' may not be null-terminated after calling 'operator='.
    * basic_string.h:705: 'this->_M_dataplus._M_p' may not be null-terminated after calling 'assign'.
      * basic_string.h:1438: 'this->_M_dataplus._M_p' may not be null-terminated after calling '_M_replace'.
        * basic_string.tcc:429: __new_size<=this->capacity() is false
        * basic_string.tcc:465: 'this->_M_dataplus._M_p' may not be null-terminated after calling '_M_mutate'.
          * basic_string.tcc:318: __pos is true
          * basic_string.tcc:319: '__r' may not be null-terminated after calling '_S_copy'.
            * basic_string.h:348: __n==1 is false
            * basic_string.h:351: '__d' may not be null-terminated after calling 'copy'.
              * char_traits.h:365: The size parameter may be less than length of source buffer.
              * char_traits.h:365: '__s1' may not be null-terminated after calling '__builtin_memcpy'.
          * basic_string.tcc:320: __len2 is false
          * basic_string.tcc:320: __s&&__len2 is false
          * basic_string.tcc:322: __how_much is false
          * basic_string.tcc:327: _M_data(__r): copies '__r' into 'this->_M_dataplus._M_p'
  * acl_hal_mmd.cpp:782: debug_verbosity>=1 is false
  * acl_hal_mmd.cpp:821: debug_verbosity>=1 is false
  * acl_hal_mmd.cpp:798: board_vendor_path.c_str(): returns 'board_vendor_path._M_dataplus._M_p'
  * acl_hal_mmd.cpp:798: String 'board_vendor_path._M_dataplus._M_p' is not properly terminated and is passed as an argument to function 'opendir'.
Current status 'Analyze'

Author: pcolberg

src/acl_hal_mmd.cpp

@@ -763,7 +763,7 @@ cl_bool l_load_board_libraries(cl_bool load_libraries) {
 cl_bool l_load_board_libraries(cl_bool load_libraries) {
   // Keeping the old path for backward compatibility
   std::string board_vendor_path_old = "/opt/Intel/OpenCL_boards/";
-  std::string board_vendor_path;
+  std::string board_vendor_path = "/opt/Intel/OpenCL/Boards/";
   auto *customer_board_vendor_path = acl_getenv("ACL_BOARD_VENDOR_PATH");
   acl_assert_locked();
 
@@ -774,9 +774,6 @@ cl_bool l_load_board_libraries(cl_bool load_libraries) {
     // append the '/' to the end of the customer_board_vendor_path
     // and load it to board_vendor_path
     board_vendor_path = customer_board_vendor_path + std::string("/");
-  } else {
-    // use the default path
-    board_vendor_path = "/opt/Intel/OpenCL/Boards/";
   }
 
   ACL_HAL_DEBUG_MSG_VERBOSE(1, "Intel(R) FPGA Board Vendor Path: %s\n",