<filename>configure</filename> will pick
     <filename>gcc</filename> if available, else the platform's
     default (usually <filename>cc</filename>).  Similarly, you can override the
     default compiler flags if needed with the <envar>CFLAGS</envar> variable.
    </para>

    <para>
     Here is a list of the significant variables that can be set in
     this manner:

     <variablelist>
      <varlistentry id="configure-envvars-bison">
       <term><envar>BISON</envar></term>
       <listitem>
        <para>
         Bison program
        </para>
       </listitem>
      </varlistentry>

      <varlistentry id="configure-envvars-cc">
       <term><envar>CC</envar></term>
       <listitem>
        <para>
         C compiler
        </para>
       </listitem>
      </varlistentry>

      <varlistentry id="configure-envvars-cflags">
       <term><envar>CFLAGS</envar></term>
       <listitem>
        <para>
         options to pass to the C compiler
        </para>
       </listitem>
      </varlistentry>

      <varlistentry id="configure-envvars-clang">
       <term><envar>CLANG</envar></term>
       <listitem>
        <para>
         path to <command>clang</command> program used to process source code
         for inlining when compiling with <literal>--with-llvm</literal>
        </para>
       </listitem>
      </varlistentry>

      <varlistentry id="configure-envvars-cpp">
       <term><envar>CPP</envar></term>
       <listitem>
        <para>
         C preprocessor
        </para>
       </listitem>
      </varlistentry>

      <varlistentry id="configure-envvars-cppflags">
       <term><envar>CPPFLAGS</envar></term>
       <listitem>
        <para>
         options to pass to the C preprocessor
        </para>
       </listitem>
      </varlistentry>

      <varlistentry id="configure-envvars-cxx">
       <term><envar>CXX</envar></term>
       <listitem>
        <para>
         C++ compiler
        </para>
       </listitem>
      </varlistentry>

      <varlistentry id="configure-envvars-cxxflags">
       <term><envar>CXXFLAGS</envar></term>
       <listitem>
        <para>
         options to pass to the C++ compiler
        </para>
       </listitem>
      </varlistentry>

      <varlistentry id="configure-envvars-dtrace">
       <term><envar>DTRACE</envar></term>
       <listitem>
        <para>
         location of the <command>dtrace</command> program
        </para>
       </listitem>
      </varlistentry>

      <varlistentry id="configure-envvars-dtraceflags">
       <term><envar>DTRACEFLAGS</envar></term>
       <listitem>
        <para>
         options to pass to the <command>dtrace</command> program
        </para>
       </listitem>
      </varlistentry>

      <varlistentry id="configure-envvars-flex">
       <term><envar>FLEX</envar></term>
       <listitem>
        <para>
         Flex program
        </para>
       </listitem>
      </varlistentry>

      <varlistentry id="configure-envvars-ldflags">
       <term><envar>LDFLAGS</envar></term>
       <listitem>
        <para>
         options to use when linking either executables or shared libraries
        </para>
       </listitem>
      </varlistentry>

      <varlistentry id="configure-envvars-ldflags-ex">
       <term><envar>LDFLAGS_EX</envar></term>
       <listitem>
        <para>
         additional options for linking executables only
        </para>
       </listitem>
      </varlistentry>

      <varlistentry id="configure-envvars-ldflags-sl">
       <term><envar>LDFLAGS_SL</envar></term>
       <listitem>
        <para>
         additional options for linking shared libraries only
        </para>
       </listitem>
      </varlistentry>

      <varlistentry id="configure-envvars-llvm-config">
       <term><envar>LLVM_CONFIG</envar></term>
       <listitem>
        <para>
         <command>llvm-config</command> program used to locate the
         <productname>LLVM</productname> installation
        </para>
       </listitem>
      </varlistentry>