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='2023-06-12 18:12:39 +0300'>2023-06-12</span></td><td><a href='/guix/commit/gnu/packages/patches/directfb-davinci-glibc-228-compat.patch?id=3fc26c6dc4b6bbf558a17b5e3ef8092ea0eeeacd'>gnu: directfb: Fix building on armhf-linux.</a><span class='msg-avail'>...<span class='msg-tooltip'>* gnu/packages/graphics.scm (directfb)[arguments]: Add a phase when
building for armhf-linux to apply a patch.
[native-inputs]: Add patch, patch file.
* gnu/packages/patches/directfb-davinci-glibc-228-compat.patch: New file.
* gnu/local.mk (dist_patch_DATA): Register it.
</span></span></td><td>Efraim Flashner</td></tr>