From:- http://www.mozilla.org/ports/os2/gccsetup.html

Download the following packages:

    * EMX Runtime
      Unzip EMXRT.ZIP in the root directory. It will create a directory called EMX.
      Add D:\EMX\DLL to your LIBPATH in CONFIG.SYS.
    * autoconf
      Unzip AUTOCONF.ZIP in the root directory. It will create a directory called AUTOCONF.
    * glib and libidl
      Unzip GLIBIDL.ZIP in the root directory. It will create a directory called GLIBIDL.
    * Perl 5.8.0 (bin & core)
      Unzip both zips in the root directory.  It will create a directory called PERL.
      In the file PERL\LIB\5.8.0\OS2\CONFIG.PM,  find the "archlib"  tag (line 120) and change the drive letter to point to where you have installed PERL.

Note:For the following packages, you only need to extract the files we specify from the ZIPs. We recommend putting all of the following EXEs and DLLs in one directory called MOZTOOLS.

    * CVS
          o cvs.exe
    * NSINSTALL
          o nsinstall.exe
    * BSD Ash
          o ash.exe
    * GNU shell utilities (sh-utils-2.0.zip)
          o Unzip OS2TREE.ZIP
          o Copy everything in USR\BIN and USR\DLL to your MOZTOOLS dir.
    * GNU text utilities (textutils-2.0.11.zip)
          o Unzip OS2TREE.ZIP
          o Copy everything in USR\BIN and USR\DLL to your MOZTOOLS dir.
    * GNU file utilities (os2_fileutils-3.16.zip)
          o Copy everything in FILEUTILS-3.16\BIN and FILEUTILS-3.16\DLL to your MOZTOOLS dir.
    * GNU diff (diffutils-2.8.zip)
          o Unzip OS2TREE.ZIP
          o Copy everything in USR\BIN to your MOZTOOLS dir.
    * GNU grep (grep-2_5_1-bin.zip)
          o Copy everything in BIN to your MOZTOOLS dir.
    * GNU awk (gawk304.zip)
          o Unzip EMX-GAWK.ZIP
          o Copy EMX\BIN\GAWK.EXE to your MOZTOOLS dir.
          o Copy gawk.exe to awk.exe
    * GNU m4 v1.4
          o m4.exe
    * GNU make 3.81
          o make.exe
    * gettext-0_11_5-r2-bin.zip
          o intl.dll
    * GNU sed v4.0.5
          o sed.exe
    * GNU find v4.1
          o find.exe
          o xargs.exe
          o gnufind.dll
          o gnuregex.dll
          o Copy gnuregex.dll to regex.dll (the latter is needed by grep.exe)
    * Info-ZIP (Zip and UnZip)
          o zip.exe
          o unzip.exe
    * RC.EXE                   <= use this one, rather than the one that comes with the toolkit
    * ILINK 5.0
          o Copy everything in BIN to your MOZTOOLS dir.
    * GNU Patch v2.5
          o patch.exe
          o Use the unrpm script to extract the executable.
    * GNU Tar v1.10
          o tar.exe
    * Icon converter version 0.92-2
          o winico.exe

GCC 3.2.2

Download GCC 3.2.2 Beta 4 from the Innotek site and install it. Then download the latest update, GCC 3.2.2 Beta 4 CSD 1, and unpack on top of this installation. Then go into the lib directory and run MakeOmfLibs.cmd. The rest of the instructions assume you installed into the directory D:\GCC322. If you installed elsewhere, you will have to make the appropriate changes.
OS/2 Toolkit
Install the Toolkit that comes with your version of Warp.

Part Two - Build it

Step 1:  Setup the environment using the setmozenv.cmd file. Just run:

    * setmozenv gcc

eComStation users might need to add a line 'SET PROGRAMS=' to setmozenv.cmd to delete this environment variable that interferes with some makefile operation.

Step 2:  Prepare pulling the code:

    * cvs co mozilla/client.mk
    * cd mozilla

Step 3:  Generate the .mozconfig file, which is a file you create in the mozilla directory that specifies options for the build. Some of the more common options are creating an obj directory which separates the source code from the built code or enabling security. To create a .mozconfig file, see the Unix Build Configurator at http://webtools.mozilla.org/build/config.cgi

We strongly recommend that you build with an obj directory

Here is what our typical .mozconfig file look like for a debug build of the Mozilla Suite:

# sh
# Build configuration script
#
# See http://www.mozilla.org/build/unix.html for build instructions.
#

# Options for client.mk.
mk_add_options MOZ_OBJDIR=@TOPSRCDIR@/obj
mk_add_options MOZ_CO_PROJECT=suite

# Options for 'configure' (same as command-line options).
ac_add_options --enable-application=suite
#ac_add_options --disable-tests
#ac_add_options --enable-optimize
#ac_add_options --disable-debug
ac_add_options --enable-crypto

If you want to build Firefox or Thunderbird, take a look at the build options page at http://www.mozilla.org/build/configure-build.html

Step 4:  Now pull the code from the CVS repository at mozilla.org:

    * make -f client.mk pull_all

Step 5:  Although the pull_all command above should do this automatically, it is sometimes necessary to delete the three configure files so that they can be properly generated on OS/2. This usually happens when there is a CVS conflict when pulling the code. If you encounter errors during the build, you should first try deleting the configure files before asking for help in netscape.public.mozilla.os2:

    * rm mozilla/configure
    * rm mozilla/nsprpub/configure
    * rm mozilla/directory/c-sdk/configure

These will be regenerated automatically from the corresponding configure.in file when you kick off the build in the next step. To generate them manually, go to each directory and run 'bash autoconf'.

Step 6:  Build the code:

    * make -f client.mk build