Watcom: Simplify compiler version detection (#11866)

Since commit c198730b (Detect Watcom compiler version with its id,
2011-12-07) the CMAKE_(C|CXX)_COMPILER_VERSION variables are set for the
Watcom compiler.  Use these in Windows-wcl386.cmake to set the old
WATCOM1* version variables.  This avoids using the old EXECUTE_PROCESS
command which failed due to extra quotes anyway.

Modules/Platform/Windows-wcl386.cmake

@@ -83,40 +83,27 @@ SET(CMAKE_CXX_CREATE_STATIC_LIBRARY  "wlib ${CMAKE_LIB_QUIET} -c -n -b '<TARGET_
 # create a C static library
 SET(CMAKE_C_CREATE_STATIC_LIBRARY ${CMAKE_CXX_CREATE_STATIC_LIBRARY})
 
-IF(NOT CMAKE_WATCOM_COMPILER_TESTS_RUN)
-  SET(CMAKE_WATCOM_COMPILER_TESTS_RUN 1)
-  SET(testWatcomVersionFile
-    "${CMAKE_ROOT}/Modules/CMakeTestWatcomVersion.c")
-  STRING(REGEX REPLACE "/" "\\\\" testWatcomVersionFile "${testWatcomVersionFile}")
-  MESSAGE(STATUS "Check for Watcom compiler version")
-  SET(CMAKE_TEST_COMPILER ${CMAKE_C_COMPILER})
-  IF (NOT CMAKE_C_COMPILER)
-    SET(CMAKE_TEST_COMPILER ${CMAKE_CXX_COMPILER})
-  ENDIF()
-  EXECUTE_PROCESS(COMMAND ${CMAKE_TEST_COMPILER}
-    -q -pc \"${testWatcomVersionFile}\"
-    OUTPUT_VARIABLE CMAKE_COMPILER_OUTPUT
-    RESULT_VARIABLE CMAKE_COMPILER_RETURN
-    )
-  STRING(REGEX REPLACE "\n" " " compilerVersion "${CMAKE_COMPILER_OUTPUT}")
-  STRING(REGEX REPLACE ".*VERSION=(.*)" "\\1"
-    compilerVersion "${compilerVersion}")
-  IF("${CMAKE_COMPILER_RETURN}" STREQUAL "0")
-    SET(WATCOM16)
-    SET(WATCOM17)
-    SET(WATCOM18)
-    SET(WATCOM19)
-    IF("${compilerVersion}" LESS 1270)
-      SET(WATCOM16 1)
-    ENDIF()
-    IF("${compilerVersion}" EQUAL 1270)
-      SET(WATCOM17 1)
-    ENDIF()
-    IF("${compilerVersion}" EQUAL 1280)
-      SET(WATCOM18 1)
-    ENDIF()
-    IF("${compilerVersion}" EQUAL 1290)
-      SET(WATCOM19 1)
-    ENDIF()
-  ENDIF()
-ENDIF()
+if(NOT _CMAKE_WATCOM_VERSION)
+  set(_CMAKE_WATCOM_VERSION 1)
+  if(CMAKE_C_COMPILER_VERSION)
+    set(_compiler_version ${CMAKE_C_COMPILER_VERSION})
+  else()
+    set(_compiler_version ${CMAKE_CXX_COMPILER_VERSION})
+  endif()
+  set(WATCOM16)
+  set(WATCOM17)
+  set(WATCOM18)
+  set(WATCOM19)
+  if("${_compiler_version}" LESS 12.70)
+    set(WATCOM16 1)
+  endif()
+  if("${_compiler_version}" EQUAL 12.70)
+    set(WATCOM17 1)
+  endif()
+  if("${_compiler_version}" EQUAL 12.80)
+    set(WATCOM18 1)
+  endif()
+  if("${_compiler_version}" EQUAL 12.90)
+    set(WATCOM19 1)
+  endif()
+endif()