gnu: Require NEON on armhf.

* gnu/packages/gcc.scm (gcc-configure-flags-for-triplet): On armhf,
  include --with-fpu=neon.
* doc/guix.texi (GNU Distribution): Document that our armhf port
  requires NEON.

doc/guix.texi

@@ -4428,7 +4428,7 @@ Intel/AMD @code{x86_64} architecture, Linux-Libre kernel;
 Intel 32-bit architecture (IA32), Linux-Libre kernel;
 
 @item armhf-linux
-ARMv7-A architecture with hard float, Thumb-2 and VFP3D16 coprocessor,
+ARMv7-A architecture with hard float, Thumb-2 and NEON,
 using the EABI hard-float ABI, and Linux-Libre kernel.
 
 @item mips64el-linux

gnu/packages/gcc.scm

@@ -55,9 +55,7 @@ (define (gcc-configure-flags-for-triplet target)
          '("--with-arch=armv7-a"
            "--with-float=hard"
            "--with-mode=thumb"
-
-           ;; See <https://wiki.debian.org/ArmHardFloatPort/VfpComparison#FPU>
-           "--with-fpu=vfpv3-d16"))
+           "--with-fpu=neon"))
 
         (else
          ;; TODO: Add `arm.*-gnueabi', etc.