Prevent implicit conversion of float to double to avoid precision
error on i686.

  https://github.com/Maratyszcza/FP16/issues/20

Taken from Debian:

  https://salsa.debian.org/deeplearning-team/fp16/-/blob/master/debian/patches/ftbfs-i386.patch

Index: fp16/include/fp16/fp16.h
===================================================================
--- fp16.orig/include/fp16/fp16.h
+++ fp16/include/fp16/fp16.h
@@ -228,7 +228,8 @@ static inline uint16_t fp16_ieee_from_fp
 	const float scale_to_inf = fp32_from_bits(UINT32_C(0x77800000));
 	const float scale_to_zero = fp32_from_bits(UINT32_C(0x08800000));
 #endif
-	float base = (fabsf(f) * scale_to_inf) * scale_to_zero;
+	const volatile float base_inf = fabsf(f) * scale_to_inf;
+	float base = base_inf * scale_to_zero;
 
 	const uint32_t w = fp32_to_bits(f);
 	const uint32_t shl1_w = w + w;
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<tr><td><span title='2021-02-22 20:44:58 +0000'>2021-02-22</span></td><td><a href='/guix/commit/gnu/system/hurd.scm?id=7c5e5e0e0fbf11ebaaeb8f98ed6c75289ca31795'>system: hurd: Have the static networking provision 'networking.</a><span class='msg-avail'>...</span></td><td>Christopher Baines</td></tr>
<tr><td><span title='2020-10-09 23:25:34 +0200'>2020-10-09</span></td><td><a href='/guix/commit/gnu/system/hurd.scm?id=d56d79b17630aa6849503db6c6f3a2a649c6ca33'>system: hurd: Add diffutils, patch, gawk, tar, gzip, bzip2, xz, and lzip.</a><span class='msg-avail'>...</span></td><td>Jan (janneke) Nieuwenhuizen</td></tr>
<tr><td><span title='2020-10-09 23:25:33 +0200'>2020-10-09</span></td><td><a href='/guix/commit/gnu/system/hurd.scm?id=1103f878054a3da5c579b1144defd0014abff775'>system: hurd: Include 'guile-3.0-latest' in '%base-packages/hurd'.</a><span class='msg-avail'>...</span></td><td>Jan (janneke) Nieuwenhuizen</td></tr>
<tr><td><span title='2020-10-09 23:25:33 +0200'>2020-10-09</span></td><td><a href='/guix/commit/gnu/system/hurd.scm?id=16f8ea064cde3ee4ef36212cdbdef90e98ba6914'>system: hurd: Add PAM support with shadow and sudo.</a><span class='msg-avail'>...</span></td><td>Jan (janneke) Nieuwenhuizen</td></tr>