https://github.com/rnpgp/rnp/pull/2209
GoogleTest 1.14.0 requires C++ 14:

[   26s] /usr/include/gtest/internal/gtest-port.h:279:2: error: #error C++ versions less than C++14 are not supported.
[   26s]   279 | #error C++ versions less than C++14 are not supported.
[   26s]       |  ^~~~~

Index: rnp-v0.17.0/CMakeLists.txt
===================================================================
--- rnp-v0.17.0.orig/CMakeLists.txt
+++ rnp-v0.17.0/CMakeLists.txt
@@ -137,7 +137,7 @@ endif(WIN32)
 
 # set a few other things at the top level to prevent incompatibilities
 set(CMAKE_C_STANDARD 99)
-set(CMAKE_CXX_STANDARD 11)
+set(CMAKE_CXX_STANDARD 14)
 set(CMAKE_CXX_STANDARD_REQUIRED ON)
 set(CMAKE_CXX_EXTENSIONS OFF)
 add_definitions(-D_GNU_SOURCE)