Add a README.md for building Android's GCC.
Bug: http://b/25191787
Change-Id: Ifa79236dd144496419f079ddac18259ead607844
diff --git a/README.md b/README.md
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+Building GCC for Android
+========================
+
+The following process is used to build the GCC that is used by both the Android
+platfrom and the NDK.
+
+Both Linux and Windows toolchains are built on Linux machines. Windows host
+binaries are built with mingw. Building binaries for Mac OS X should be built
+using 10.8 to ensure compatibility with Android's minimum supported hosts.
+
+Prerequisites
+-------------
+
+* [Android GCC Repository](http://source.android.com/source/downloading.html)
+ * Check out the branch `gcc`
+
+ ```bash
+ repo init -u https://android.googlesource.com/platform/manifest -b gcc
+
+ # Googlers, use
+ repo init -u \
+ persistent-https://android.git.corp.google.com/platform/manifest \
+ -b gcc
+ ```
+
+* Additional Linux Dependencies (available from apt):
+ * texinfo
+ * gcc-mingw32
+ * bison
+ * flex
+ * libtool
+* Mac OS X also requires Xcode.
+
+Host/Target prebuilts
+---------------------
+
+### For Linux or Darwin:
+
+```bash
+# Additional options and toolchain names will be show with --help.
+$ python build.py --toolchain TOOLCHAIN_NAME
+```
+
+### For Windows, from Linux:
+
+```bash
+$ python build.py --system windows TOOLCHAIN_NAME
+```
