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.

build-libraries.sh

@@ -13,7 +13,7 @@ TARGET="arm-uclinuxfdpiceabi"
 TOOLCHAIN="${TARGET}"
 TOOLCHAIN_PATH="${INSTALL_DIR}/bin"
 CFLAGS_TOOLSET='-O2'
-CFLAGS_TARGET='-Os -mthumb'
+CFLAGS_TARGET='-Os -mthumb -mcpu=cortex-m7 -mfpu=fpv5-d16 -mfloat-abi=hard'
 _ORIG_PATH="$PATH"
 
 export SYSROOT="${SYSROOT_DIR}"
@@ -38,7 +38,7 @@ export LDFLAGS=""
 export CFLAGS_FOR_TARGET="${CFLAGS_TARGET}"
 export CXXFLAGS_FOR_TARGET="${CFLAGS_TARGET}"
 export LDFLAGS_FOR_TARGET='-Wl,--fdpic'
-export SUBARCH=armv7-m
+export SUBARCH=armv7e-m
 export SUBMODE=thumb
 export PATH="${TOOLCHAIN_PATH}:${_ORIG_PATH}"