fix(mingw): only fall back on JWASM if no other ASM_MASM has been specified (#133)

Author: supervacuus

CMakeLists.txt

@@ -57,19 +57,22 @@ if(WIN32 AND NOT (MINGW AND "${CMAKE_SYSTEM_PROCESSOR}" MATCHES "[Aa][Rr][Mm]64"
     endif()
 
     if(MINGW)
-        find_program(JWASM_FOUND jwasm)
-        if (JWASM_FOUND)
-            set(CMAKE_ASM_MASM_COMPILER ${JWASM_FOUND})
-            execute_process(COMMAND ${CMAKE_C_COMPILER} --version OUTPUT_VARIABLE COMPILER_VERSION_OUTPUT)
-            if (COMPILER_VERSION_OUTPUT)
-                if (COMPILER_VERSION_OUTPUT MATCHES "x86_64")
-                    set(JWASM_FLAGS -win64)
-                else()
-                    set(JWASM_FLAGS -coff)
+        if(NOT DEFINED CMAKE_ASM_MASM_COMPILER OR CMAKE_ASM_MASM_COMPILER STREQUAL "")
+            # Only check for and set up JWASM if no ASM_MASM has been specified before
+            find_program(JWASM_FOUND jwasm)
+            if (JWASM_FOUND)
+                set(CMAKE_ASM_MASM_COMPILER ${JWASM_FOUND})
+                execute_process(COMMAND ${CMAKE_C_COMPILER} --version OUTPUT_VARIABLE COMPILER_VERSION_OUTPUT)
+                if (COMPILER_VERSION_OUTPUT)
+                    if (COMPILER_VERSION_OUTPUT MATCHES "x86_64")
+                        set(JWASM_FLAGS -win64)
+                    else()
+                        set(JWASM_FLAGS -coff)
+                    endif()
                 endif()
-            endif()
-           set(CMAKE_ASM_MASM_FLAGS ${CMAKE_ASM_MASM_FLAGS} ${JWASM_FLAGS})
-        endif(JWASM_FOUND)
+                set(CMAKE_ASM_MASM_FLAGS ${CMAKE_ASM_MASM_FLAGS} ${JWASM_FLAGS})
+            endif(JWASM_FOUND)
+        endif()
 
         if(NOT CMAKE_ASM_MASM_COMPILER OR CMAKE_ASM_MASM_COMPILER STREQUAL "ml" OR CMAKE_ASM_MASM_COMPILER STREQUAL "ml64")
             message(WARNING "No custom ASM_MASM compiler defined via 'CMAKE_ASM_MASM_COMPILER'. Trying to use UASM...")