Check for cbrtf() and provide fallback

(cherry picked from commit bfb37d7db1c6394099f6b177e10d6e769e678f6a)
Signed-off-by: Michael Niedermayer <michaelni@gmx.at>

configure

@@ -1125,6 +1125,7 @@ HAVE_LIST="
     attribute_may_alias
     attribute_packed
     bswap
+    cbrtf
     closesocket
     cmov
     dcbzl
@@ -2999,6 +3000,7 @@ check_lib math.h sin -lm && LIBM="-lm"
 disabled crystalhd || check_lib libcrystalhd/libcrystalhd_if.h DtsCrystalHDVersion -lcrystalhd || disable crystalhd
 enabled vaapi && require vaapi va/va.h vaInitialize -lva
 
+check_mathfunc cbrtf
 check_mathfunc exp2
 check_mathfunc exp2f
 check_mathfunc llrint

libavutil/libm.h

@@ -28,6 +28,11 @@
 #include "config.h"
 #include "attributes.h"
 
+#if !HAVE_CBRTF
+#undef cbrtf
+#define cbrtf(x) powf(x, 1.0/3.0)
+#endif /* HAVE_CBRTF */
+
 #if !HAVE_EXP2
 #undef exp2
 #define exp2(x) exp((x) * 0.693147180559945)