pixman-private: include <float.h> only in C code

<float.h> is included unconditionally by pixman-private.h, which in
turn gets included by assembler files. Unfortunately, with certain C
libraries (like the musl C library), <float.h> cannot be included in
assembler files:

  CCLD     libpixman-arm-simd.la
/home/test/buildroot/output/host/usr/arm-buildroot-linux-musleabihf/sysroot/usr/include/float.h: Assembler messages:
/home/test/buildroot/output/host/usr/arm-buildroot-linux-musleabihf/sysroot/usr/include/float.h:8: Error: bad instruction `int __flt_rounds(void)'
/home/test/buildroot/output/host/usr/arm-buildroot-linux-musleabihf/sysroot/usr/include/float.h: Assembler messages:
/home/test/buildroot/output/host/usr/arm-buildroot-linux-musleabihf/sysroot/usr/include/float.h:8: Error: bad instruction `int __flt_rounds(void)'

It turns out however that <float.h> is not needed by assembly files,
so we move its inclusion within the #ifndef __ASSEMBLER__ condition,
which solves the problem.

Signed-off-by: Thomas Petazzoni <thomas.petazzoni@free-electrons.com>
Reviewed-by: Siarhei Siamashka <siarhei.siamashka@gmail.com>
diff --git a/pixman/pixman-private.h b/pixman/pixman-private.h
index 73108a0..73a5414 100644
--- a/pixman/pixman-private.h
+++ b/pixman/pixman-private.h
@@ -1,5 +1,3 @@
-#include <float.h>
-
 #ifndef PIXMAN_PRIVATE_H
 #define PIXMAN_PRIVATE_H
 
@@ -30,6 +28,7 @@
 #include <stdio.h>
 #include <string.h>
 #include <stddef.h>
+#include <float.h>
 
 #include "pixman-compiler.h"