Rename FindNettle and FindSeccomp to FindNETTLE and FindSECCOMP.

CMake 3.17's FIND_PACKAGE() is complaining that the package name
doesn't match the filename. Rename the filenames to match.

CMakeLists.txt

@@ -14,7 +14,6 @@ ENDIF(NOT CMAKE_PROJECT_VERSION OR NOT CMAKE_PROJECT_VERSION_MAJOR)
 
 LIST(APPEND CMAKE_MODULE_PATH
 	"${CMAKE_SOURCE_DIR}/cmake/macros"
-	"${CMAKE_SOURCE_DIR}/cmake/modules"
 	"${CMAKE_SOURCE_DIR}/cmake/libs"
 	)
 IF(UNIX AND NOT APPLE)

src/librpbase/CMakeLists.txt

@@ -23,7 +23,7 @@ IF(NOT WIN32)
 	ENDIF(NOT Iconv_IS_BUILT_IN)
 
 	IF(ENABLE_DECRYPTION)
-		FIND_PACKAGE(Nettle REQUIRED)
+		FIND_PACKAGE(NETTLE REQUIRED)
 		SET(HAVE_NETTLE ${NETTLE_FOUND})
 		IF(HAVE_NETTLE)
 			# Check if this is Nettle 3.x.

src/librpsecure/CMakeLists.txt

@@ -32,7 +32,7 @@ ELSEIF(UNIX AND NOT APPLE)
 	# Check for system security functionality.
 	IF(USE_SECCOMP)
 		# Linux: Use seccomp().
-		FIND_PACKAGE(Seccomp REQUIRED)
+		FIND_PACKAGE(SECCOMP REQUIRED)
 		IF(SECCOMP_FOUND)
 			SET(librpsecure_OS_SRCS os-secure_linux.c)
 			IF(ENABLE_SECCOMP_DEBUG)