FTBFS against gcc 11 on armhf

[Dan Bungert]

While tracing the build failure of rust-curl-sys on armhf, I observed that both rust-curl-sys and rust-openssl-sys will FTBFS with gcc-11. gcc-10 seems fine.

https://autopkgtest.ubuntu.com/results/autopkgtest-impish/impish/armhf/r/rust-curl-sys/20210819_074312_77b43@/log.gz

I was able to verify this locally in an impish armhf container running on raspberry pi 4, and also in PPA builds.
gcc 10: https://launchpadlibrarian.net/555621807/buildlog_ubuntu-impish-armhf.rust-openssl-sys_0.9.55-2ppa1_BUILDING.txt.gz
gcc 11: https://launchpadlibrarian.net/555622883/buildlog_ubuntu-impish-armhf.rust-openssl-sys_0.9.55-2ppa2_BUILDING.txt.gz

[Steve Langasek (vorlon)]

[openssl-sys 0.9.55] running: "cc" "-O0" "-ffunction-sections" "-fdata-sections"
 "-fPIC" "-g" "-fno-omit-frame-pointer" "-march=armv7-a" "-g" "-O2" "-ffile-pref
ix-map=/usr/share/cargo/registry/openssl-sys-0.9.55=." "-fstack-protector-strong
" "-Wformat" "-Werror=format-security" "-I" "/usr/include" "-E" "build/expando.c
"
[openssl-sys 0.9.55] cargo:warning=cc1: error: ‘-mfloat-abi=hard’: selected architecture lacks an FPU

This is actually a bug in gcc-11, which had the wrong target. It is fixed by the gcc-11 in -proposed.