added a bare fftw3 test in order to make sure fftw3 works on a new platform.

src/tests/fftw3_bare/CMakeLists.txt

@@ -0,0 +1,51 @@
+cmake_minimum_required(VERSION 3.9)
+
+project(fftw3_test VERSION 0.1 LANGUAGES C CXX)
+
+#--- set a default build type if none was specified ---------------------------
+set(default_build_type "Debug")
+
+#--- the next two lines are needed that the math functions are found ----------
+set(CMAKE_REQUIRED_INCLUDES math.h)
+set(CMAKE_REQUIRED_LIBRARIES m) 
+
+include(CheckTypeSize)
+include(CheckIncludeFiles)
+include(CheckFunctionExists)
+check_include_files(alloca.h HAVE_ALLOCA_H)
+check_include_files("sys/ipc.h;sys/shm.h" HAVE_SHMGET)
+check_include_files(dlfcn.h HAVE_DLFCN_H)
+check_function_exists(erf HAVE_ERF)
+check_function_exists(getloadavg HAVE_GETLOADAVG)
+check_include_files(inttypes.h HAVE_INTTYPES_H)
+check_include_files(memory.h HAVE_MEMORY_H)
+check_function_exists(powl HAVE_POWL)
+check_include_files(memory.h HAVE_MEMORY_H)
+check_include_files(stdint.h HAVE_STDINT_H)
+check_include_files(stdlib.h HAVE_STDLIB_H)
+check_include_files(string.h HAVE_STRING_H)
+check_include_files(strings.h HAVE_STRINGS_H)
+check_include_files(sys/stat.h HAVE_SYS_STAT_H)
+check_include_files(sys/types.h HAVE_SYS_TYPES_H)
+check_include_files(sys/unistd.h HAVE_UNISTD_H)
+check_type_size("long double" LONG_DOUBLE)
+check_type_size("double" DOUBLE)
+if (${LONG_DOUBLE} GREATER ${DOUBLE})
+  set(HAVE_LONG_DOUBLE 1)
+  set(HAVE_LONG_DOUBLE_WIDER 1)
+endif (${LONG_DOUBLE} GREATER ${DOUBLE})
+
+#--- add path to my own find modules and other stuff
+set(CMAKE_MODULE_PATH ${CMAKE_CURRENT_SOURCE_DIR}/../../../cmake)
+
+#--- check for fftw3 ----------------------------------------------------------
+find_package(FFTW3 REQUIRED)
+message(" FFTW3_INCLUDE_DIR: ${FFTW3_INCLUDE_DIR}")
+message(" FFTW3_LIBRARY    : ${FFTW3_LIBRARY}")
+
+add_executable(fftw3_test fftw3_test.cpp)
+target_include_directories(fftw3_test
+  BEFORE PRIVATE
+    $<BUILD_INTERFACE:${FFTW3_INCLUDE_DIR}>
+)
+target_link_libraries(fftw3_test ${FFTW3_LIBRARY})