libgcc/config/arm/fp16.c: Make _internal functions static inline

libgcc/config/arm/fp16.c: Make _internal functions static inline

This patch makes the *_internal functions 'static inline' to avoid these warnings during the build:
/libgcc/config/arm/fp16.c:169:1: warning: no previous prototype for '__gnu_h2f_internal' [-Wmissing-prototypes]
/libgcc/config/arm/fp16.c:194:1: warning: no previous prototype for '__gnu_f2h_ieee' [-Wmissing-prototypes]
/libgcc/config/arm/fp16.c:200:1: warning: no previous prototype for '__gnu_h2f_ieee' [-Wmissing-prototypes]
/libgcc/config/arm/fp16.c:206:1: warning: no previous prototype for '__gnu_f2h_alternative' [-Wmissing-prototypes]
/libgcc/config/arm/fp16.c:212:1: warning: no previous prototype for '__gnu_h2f_alternative' [-Wmissing-prototypes]
/libgcc/config/arm/fp16.c:218:1: warning: no previous prototype for '__gnu_d2h_ieee' [-Wmissing-prototypes]
/libgcc/config/arm/fp16.c:224:1: warning: no previous prototype for '__gnu_d2h_alternative' [-Wmissing-prototypes]

2020-09-11  Torbjörn SVENSSON  <torbjorn.svensson@st.com>
	    Christophe Lyon  <christophe.lyon@linaro.org>

	libgcc/
	* config/arm/fp16.c (__gnu_h2f_internal): Add 'static inline'
	qualifier.
	(__gnu_f2h_ieee, __gnu_h2f_ieee, __gnu_f2h_alternative)
	(__gnu_h2f_alternative,__gnu_d2h_ieee, __gnu_d2h_alternative): Add
	missing prototypes.