Limit gcc version supported (#1451)

* tie down minimal gcc version

.CMake/compiler_opts.cmake

@@ -144,6 +144,9 @@ if(CMAKE_C_COMPILER_ID MATCHES "Clang")
     endif()
 
 elseif(CMAKE_C_COMPILER_ID STREQUAL "GNU")
+  if (NOT ${CMAKE_C_COMPILER_VERSION} VERSION_GREATER_EQUAL ${OQS_MINIMAL_GCC_VERSION})
+     message(FATAL_ERROR "GCC version ${CMAKE_C_COMPILER_VERSION} below minimally required version ${OQS_MINIMAL_GCC_VERSION}.")
+  endif()
   if(${OQS_STRICT_WARNINGS})
     add_compile_options(-Wall)
     add_compile_options(-Wextra)

CMakeLists.txt

@@ -35,6 +35,7 @@ set(CMAKE_POSITION_INDEPENDENT_CODE ON)
 set(CMAKE_C_VISIBILITY_PRESET hidden)
 set(OQS_VERSION_TEXT "0.8.0-dev")
 set(OQS_COMPILE_BUILD_TARGET "${CMAKE_SYSTEM_PROCESSOR}-${CMAKE_HOST_SYSTEM}")
+set(OQS_MINIMAL_GCC_VERSION "7.1.0")
 set(CMAKE_EXPORT_COMPILE_COMMANDS ON)
 
 # heuristic check to see whether we're running on a RaspberryPi

README.md

@@ -71,6 +71,12 @@ We realize some parties may want to deploy quantum-safe cryptography prior to th
 
 **WE DO NOT CURRENTLY RECOMMEND RELYING ON THIS LIBRARY IN A PRODUCTION ENVIRONMENT OR TO PROTECT ANY SENSITIVE DATA.** This library is meant to help with research and prototyping.  While we make a best-effort approach to avoid security bugs, this library has not received the level of auditing and analysis that would be necessary to rely on it for high security use.
 
+#### Platform limitations
+
+In order to optimize support effort,
+- not all algorithms are equally well supported on all platforms. In case of questions, it is first advised to review the [documentation files for each algorithm](docs/algorithms).
+- not all compilers are equally well supported. For example, at least v7.1.0 of the GNU compiler is required.
+
 ## Quickstart
 
 ### Linux/macOS