gnu: Add threaded variants of fftw and fftwf for Ardour and mod-host.

* gnu/packages/algebra.scm (fftw-with-threads, fftwf-with-threads): New
variables.
* gnu/packages/audio.scm (ardour)[inputs]: Replace "fftw" and "fftwf"
with "fftw-with-threads" and "fftwf-with-threads", respectively.
* gnu/packages/music.scm (mod-host)[inputs]: Likewise.

gnu/packages/algebra.scm

@@ -576,6 +576,22 @@ cosine/ sine transforms or DCT/DST).")
      (string-append (package-description fftw)
                     "  Single-precision version."))))
 
+;; FIXME: These packages are used temporarily by packages like Ardour until
+;; "--enable-flags" is added to the fftw and fftwf packages.
+(define-public fftw-with-threads
+  (package (inherit fftw)
+    (arguments
+     (substitute-keyword-arguments (package-arguments fftw)
+       ((#:configure-flags flags)
+        `(cons "--enable-threads" ,flags))))))
+
+(define-public fftwf-with-threads
+  (package (inherit fftwf)
+    (arguments
+     (substitute-keyword-arguments (package-arguments fftwf)
+       ((#:configure-flags flags)
+        `(cons "--enable-threads" ,flags))))))
+
 (define-public fftw-openmpi
   (package (inherit fftw)
     (name "fftw-openmpi")

gnu/packages/audio.scm

@@ -238,8 +238,8 @@ namespace ARDOUR { const char* revision = \"5.4\" ; }"))))
        ("lv2" ,lv2)
        ("vamp" ,vamp)
        ("curl" ,curl)
-       ("fftw" ,fftw)
-       ("fftwf" ,fftwf)
+       ("fftw" ,fftw-with-threads)
+       ("fftwf" ,fftwf-with-threads)
        ("jack" ,jack-1)
        ("serd" ,serd)
        ("sord" ,sord)

gnu/packages/music.scm

@@ -1744,8 +1744,8 @@ analogue-like user interface.")
                #t)))))
       (inputs
        `(("lilv" ,lilv)
-         ("fftw" ,fftw)
-         ("fftwf" ,fftwf)
+         ("fftw" ,fftw-with-threads)
+         ("fftwf" ,fftwf-with-threads)
          ("lv2" ,lv2)
          ("jack" ,jack-1)
          ("readline" ,readline)))