The UEFI images can be build on FreeBSD-CURRENT/amd64.

Install the following packages:
  bash
  git
  gmake
  gcc48
  nasm
  python
  py27-sqlite3

1. Checkout the bhyve UDK2014.SP1 branch from the freebsd/uefi-edk repo

  git clone -b bhyve/UDK2014.SP1 https://github.com/freebsd/uefi-edk2.git

2. Setup the build environment

  2a  Build the base tools

      bash
      export AS=/usr/local/bin/as
      export AR=/usr/local/bin/ar
      export LD=/usr/local/bin/ld
      export OBJCOPY=/usr/local/bin/objcopy
      export CC=/usr/local/bin/gcc48
      export CXX=/usr/local/bin/g++48
      gmake -C BaseTools
 
 2b Create links to toolchain

      mkdir Build
      ln -s /usr/local/bin/gcc48 Build/gcc
      ln -s /usr/local/bin/ld Build/ld
      ln -s /usr/local/bin/gmake Build/make
      ln -s /usr/local/bin/ar Build/ar
      ln -s /usr/local/bin/objcopy Build/objcopy
      ln -s /usr/local/bin/nasm Build/nasm

3. On this, and each subsequent login, start bash if not already
    in it and:

      source edksetup.sh && export GCC48_BIN=$PWD/Build/

4. To build the UEFI binary

      build -t GCC48 -a X64 -p BhyvePkg/BhyvePkgX64.dsc \
            -DDEBUG_ON_SERIAL_PORT=TRUE -D FD_SIZE_2MB

  4a To build the UEFI+CSM binary

      (cd BhyvePkg/Csm/BhyveCsm16/; gmake)
      build -t GCC48 -a X64 -p BhyvePkg/BhyvePkgX64.dsc \
            -DDEBUG_ON_SERIAL_PORT=TRUE -DCSM_ENABLE=TRUE
      
5. The output of the build is at

      Build/BhyveX64/DEBUG_GCC48/FV/BHYVE.fd

6. To clean, use the above 'build' command and add 'clean' to the end.