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]