Re-apply hard-float toolchain configuration

Re-applies the target architecture and FPU changes from cc50788
(reverted on dev in a3b718c) on top of the soft-float baseline: Cortex-M7
with hardware VFPv5 FPU (-mfloat-abi=hard), plus uClibc-ng built with
UCLIBC_HAS_FPU=y. Hard-float support and the resulting device-side fixes
are being developed here rather than on dev directly.

scripts/env.sh

@@ -1,10 +1,10 @@
 
 TOP=`pwd`
 TARGET=arm-uclinuxfdpiceabi
-CFLAGS_TOOLSET='-O2' 
-CFLAGS_TARGET='-Os -mthumb'
+CFLAGS_TOOLSET='-O2'
+CFLAGS_TARGET='-Os -mthumb -mcpu=cortex-m7 -mfpu=fpv5-d16 -mfloat-abi=hard'
 CFLAGS=$CFLAGS_TOOLSET CFLAGS_FOR_TARGET=$CFLAGS_TARGET CXXFLAGS_FOR_TARGET=$CFLAGS_TARGET
-SUBARCH=armv7-m 
-SUBMODE=thumb 
+SUBARCH=armv7e-m
+SUBMODE=thumb
 PATH=${TOP}/${TARGET}/bin:${PATH}