$NetBSD: patch-CMakeLists.txt,v 1.2 2021/04/09 11:10:35 nia Exp $

-lm is not GNU/Linux specific...

https://github.com/mborgerding/kissfft/pull/64

--- CMakeLists.txt.orig	2021-04-09 10:52:02.217349618 +0000
+++ CMakeLists.txt
@@ -105,7 +105,7 @@ endif()
 # Add GNUInstallDirs for GNU infrastructure before target)include_directories
 #
 
-if(CMAKE_SYSTEM_NAME MATCHES "^(Linux|kFreeBSD|GNU)$" AND NOT CMAKE_CROSSCOMPILING)
+if(UNIX)
     include(GNUInstallDirs)
 endif()
 
@@ -242,7 +242,7 @@ add_library(kissfft::kissfft-${KISSFFT_D
 # Build with libm (-lm) on Linux and kFreeBSD
 #
 
-if(CMAKE_SYSTEM_NAME MATCHES "^(Linux|kFreeBSD|GNU)$" AND NOT CMAKE_CROSSCOMPILING)
+if(UNIX)
     target_link_libraries(kissfft PRIVATE m)
 endif()
 
@@ -258,7 +258,7 @@ function(add_kissfft_executable NAME)
     # Build with libm (-lm) on Linux and kFreeBSD
     #
 
-    if(CMAKE_SYSTEM_NAME MATCHES "^(Linux|kFreeBSD|GNU)$" AND NOT CMAKE_CROSSCOMPILING)
+    if(UNIX)
         target_link_libraries(${NAME} PRIVATE m)
     endif()