ports: Add lib/libm/roundf.c to bare-metal Makefile's.

This function is not used by the core but having it as part of the build
allows it to be used by user C modules, or board extensions.  The linker
won't include it in the final firmware if it remains unused.

ports/esp8266/Makefile

@@ -138,6 +138,7 @@ LIB_SRC_C = $(addprefix lib/,\
 	libm/asinfacosf.c \
 	libm/atanf.c \
 	libm/atan2f.c \
+	libm/roundf.c \
 	mp-readline/readline.c \
 	netutils/netutils.c \
 	timeutils/timeutils.c \

ports/nrf/Makefile

@@ -150,6 +150,7 @@ SRC_LIB += $(addprefix lib/,\
         libm/asinfacosf.c \
         libm/atanf.c \
         libm/atan2f.c \
+        libm/roundf.c \
 	)
 
 endif

ports/qemu-arm/Makefile

@@ -90,6 +90,7 @@ LIB_SRC_C += $(addprefix lib/,\
 	libm/asinfacosf.c \
 	libm/atanf.c \
 	libm/atan2f.c \
+	libm/roundf.c \
 	utils/sys_stdio_mphal.c \
 	)
 

ports/stm32/Makefile

@@ -214,6 +214,7 @@ SRC_LIBM = $(addprefix lib/libm/,\
 	kf_tan.c \
 	log1pf.c \
 	nearbyintf.c \
+	roundf.c \
 	sf_cos.c \
 	sf_erf.c \
 	sf_frexp.c \