[fftw3] Add openmp to fftw3 (#4351)

ports/fftw3/CONTROL

@@ -1,3 +1,6 @@
 Source: fftw3
 Version: 3.3.8
 Description: FFTW is a C subroutine library for computing the discrete Fourier transform (DFT) in one or more dimensions, of arbitrary input size, and of both real and complex data (as well as of even/odd data, i.e. the discrete cosine/sine transforms or DCT/DST).
+
+Feature: openmp
+Description: Builds openmp enabled lib

ports/fftw3/omp_test.patch

@@ -0,0 +1,17 @@
+diff --git a/CMakeLists.txt b/CMakeLists.txt
+index f3cfc20..9826bff 100644
+--- a/CMakeLists.txt
++++ b/CMakeLists.txt
+@@ -385,6 +385,12 @@ if (BUILD_TESTS)
+     target_link_libraries (bench ${fftw3_lib})
+   endif ()
+ 
++  if (ENABLE_OPENMP)
++    target_link_libraries (bench ${fftw3_lib}_omp)
++  else ()
++    target_link_libraries (bench ${fftw3_lib})
++  endif ()
++
+ 
+   enable_testing ()
+ 

ports/fftw3/portfile.cmake

@@ -17,12 +17,25 @@ vcpkg_download_distfile(ARCHIVE
 
 vcpkg_extract_source_archive(${ARCHIVE})
 
+vcpkg_apply_patches(
+    SOURCE_PATH ${SOURCE_PATH}
+    PATCHES
+        ${CMAKE_CURRENT_LIST_DIR}/omp_test.patch
+)
+
+if ("openmp" IN_LIST FEATURES)
+    set(ENABLE_OPENMP ON)
+else()
+    set(ENABLE_OPENMP OFF)
+endif()
+
 foreach(PRECISION ENABLE_DEFAULT_PRECISION ENABLE_FLOAT ENABLE_LONG_DOUBLE)
 	vcpkg_configure_cmake(
 		SOURCE_PATH ${SOURCE_PATH}
 		PREFER_NINJA
 		OPTIONS 
 			-D${PRECISION}=ON
+			-DENABLE_OPENMP=${ENABLE_OPENMP}
 	)
 
 	vcpkg_install_cmake()