Handle BUILD_DADAFLOW flag dependeing on C++ std and boost::json. Instead of...

• Handle BUILD_DADAFLOW flag dependeing on C++ std and boost::json.
• Instead of find_package(OpenMP) use '-fopenmp' flag
• Add required CMake flags to debian/rules

cmake/compiler_settings.cmake

-#
-# Compiler defaults for cheetah
-#
+# Set the default build type
 if (NOT CMAKE_BUILD_TYPE)
     set(CMAKE_BUILD_TYPE "RELEASE")
 endif ()
 
+# The sub library psrdada_cpp::dadaflow requires at least std=c++20 
+if(BUILD_DADAFLOW)
+    # Here we check if the compiler (Clang and GCC) is able to support C++ 20
+    # Other compilers are not included yet
+    if(CMAKE_CXX_COMPILER_VERSION VERSION_GREATER_EQUAL 10)
+        set(CMAKE_CXX_STANDARD 20)
+        set(CMAKE_CXX_STANDARD_REQUIRED ON)
+    # Turn BUILD_DADAFLOW off when the standard is not sufficient
+    else()
+        message(WARNING "The Compiler does not support C++20, psrdada_cpp::dadaflow won't build")
+        message(WARNING "Setting BUILD_DADAFLOW=OFF")
+        set(BUILD_DADAFLOW OFF)
+    endif()
+endif()
+# Set the minimum standard when BUILD_DADAFLOW is OFF
+if(NOT BUILD_DADAFLOW)
+    set(CMAKE_CXX_STANDARD 14)
+    set(CMAKE_CXX_STANDARD_REQUIRED ON)
+endif()
+
 # Set compiler flags
-set(CMAKE_CXX_FLAGS "--std=c++${CMAKE_CXX_STANDARD} -fPIC")
+set(CMAKE_CXX_FLAGS "--std=c++${CMAKE_CXX_STANDARD} -fPIC -fopenmp")
 
 set(ARCH "broadwell" CACHE STRING "target architecture (-march=native, x86-64), defaults to broadwell")
 set(TUNE "generic" CACHE STRING "target tune architecture (-mtune=native, x86-64), defaults to generic")
@@ -19,12 +37,11 @@ if (CMAKE_CXX_COMPILER_ID MATCHES Clang)
     set(CMAKE_CXX_FLAGS "${CMAKE_CXX_FLAGS} -Werror -march=${ARCH} -mtune=${TUNE}")
 endif ()
 if (CMAKE_COMPILER_IS_GNUCXX)
-    ## -Wl,--no-as-needed avoids linker problem with libfftwf3 on ubuntu systems
     set(CMAKE_INCLUDE_SYSTEM_FLAG_CXX "-isystem")
     set(CMAKE_CXX_FLAGS "${CMAKE_CXX_FLAGS} -Wno-ignored-attributes -pthread -Werror -Wcast-align -march=${ARCH} -mtune=${TUNE}")
 endif ()
 
-set(CMAKE_CXX_FLAGS_RELEASE "-O3 -DNDEBUG -Wno-unused-local-typedefs")
+set(CMAKE_CXX_FLAGS_RELEASE "-O3 -DNDEBUG -Wno-unused-local-typedefs -fprofile-arcs -ftest-coverage")
 set(CMAKE_CXX_FLAGS_RELWITHDEBINFO "-O3 -g -Wall -Wextra -pedantic -Wno-unused-local-typedefs -fprofile-arcs -ftest-coverage")
 set(CMAKE_CXX_FLAGS_DEBUG "-O3 -g -pg -Wall -Wextra -pedantic -Wno-unused-local-typedefs -fprofile-arcs -ftest-coverage")