Fix alpine armv7 build

Reference: https://github.com/messense/rust-musl-cross/pull/34

docker/Dockerfile.j2

@@ -93,6 +93,9 @@ RUN rustup set profile minimal
 {% if "alpine" in target_file %}
 ENV USER "root"
 ENV RUSTFLAGS='-C link-arg=-s'
+{%   if "armv7" in target_file %}
+ENV CFLAGS_armv7_unknown_linux_musleabihf="-mfpu=vfpv3-d16"
+{%   endif %}
 {% elif "arm" in target_file %}
 # Install required build libs for {{ package_arch_name }} architecture.
 # To compile both mysql and postgresql we need some extra packages for both host arch and target arch

docker/armv7/Dockerfile.alpine

@@ -38,6 +38,7 @@ RUN rustup set profile minimal
 
 ENV USER "root"
 ENV RUSTFLAGS='-C link-arg=-s'
+ENV CFLAGS_armv7_unknown_linux_musleabihf="-mfpu=vfpv3-d16"
 
 # Creates a dummy project used to grab dependencies
 RUN USER=root cargo new --bin /app