fixes 1217: rocksdbjni javac and javah execute_processes fail on windows (#1218)

picking execute_process command based on OS

java/CMakeLists.txt

@@ -150,8 +150,16 @@ if(NOT EXISTS ${JAVA_ASSERTJ_JAR})
   file(RENAME ${JAVA_TMP_JAR} ${JAVA_ASSERTJ_JAR})
 endif()
 
-execute_process(COMMAND javac -cp ${JAVA_TESTCLASSPATH} -d ${PROJECT_SOURCE_DIR}/java/classes ${PROJECT_SOURCE_DIR}/java/src/main/java/org/rocksdb/util/*.java ${PROJECT_SOURCE_DIR}/java/src/main/java/org/rocksdb/*.java ${PROJECT_SOURCE_DIR}/java/src/test/java/org/rocksdb/*.java)
-execute_process(COMMAND javah -cp ${PROJECT_SOURCE_DIR}/java/classes -d ${PROJECT_SOURCE_DIR}/java/include -jni ${NATIVE_JAVA_CLASSES})
+if(WIN32)
+  set(JAVAC cmd /c javac)
+  set(JAVAH cmd /c javah)
+else()
+  set(JAVAC javac)
+  set(JAVAH javah)
+endif()
+
+execute_process(COMMAND ${JAVAC} -cp ${JAVA_TESTCLASSPATH} -d ${PROJECT_SOURCE_DIR}/java/classes ${PROJECT_SOURCE_DIR}/java/src/main/java/org/rocksdb/util/*.java ${PROJECT_SOURCE_DIR}/java/src/main/java/org/rocksdb/*.java ${PROJECT_SOURCE_DIR}/java/src/test/java/org/rocksdb/*.java)
+execute_process(COMMAND ${JAVAH} -cp ${PROJECT_SOURCE_DIR}/java/classes -d ${PROJECT_SOURCE_DIR}/java/include -jni ${NATIVE_JAVA_CLASSES})
 add_library(rocksdbjni${ARTIFACT_SUFFIX} SHARED ${JNI_NATIVE_SOURCES})
 set_target_properties(rocksdbjni${ARTIFACT_SUFFIX} PROPERTIES COMPILE_FLAGS "/Fd${CMAKE_CFG_INTDIR}/rocksdbjni${ARTIFACT_SUFFIX}.pdb")
 target_link_libraries(rocksdbjni${ARTIFACT_SUFFIX} rocksdblib${ARTIFACT_SUFFIX} ${LIBS})