CMakeLists.txt: fix if's

CMakeLists.txt

@@ -41,18 +41,18 @@ else ()
     link_libraries(rt)
 
     check_include_files(sys/signalfd.h HAVE_SYS_SIGNALFD_H)
-    if (NOT ${HAVE_SYS_SIGNALFD_H})
+    if (NOT HAVE_SYS_SIGNALFD_H)
         message(FATAL_ERROR "signalfd is required")
     endif ()
 
     check_include_files(sys/epoll.h HAVE_SYS_EPOLL_H)
-    if (NOT ${HAVE_SYS_EPOLL_H})
+    if (NOT HAVE_SYS_EPOLL_H)
         message(FATAL_ERROR "epoll is required")
     endif ()
 
     if (NOT DEFINED BADVPN_WITHOUT_CRYPTODEV)
         check_include_files(crypto/cryptodev.h HAVE_CRYPTO_CRYPTODEV_H)
-        if (${HAVE_CRYPTO_CRYPTODEV_H})
+        if (HAVE_CRYPTO_CRYPTODEV_H)
             add_definitions(-DBADVPN_USE_CRYPTODEV)
         elseif (DEFINED BADVPN_WITH_CRYPTODEV)
             message(FATAL_ERROR "crypto/cryptodev.h not found")
@@ -61,7 +61,7 @@ else ()
 endif ()
 
 # add preprocessor definitions
-if (${BIG_ENDIAN})
+if (BIG_ENDIAN)
     add_definitions(-DBADVPN_BIG_ENDIAN)
 else ()
     add_definitions(-DBADVPN_LITTLE_ENDIAN)