ARROW-902: [C++] Script for downloading all thirdparty build dependencies and configuration for offline builds

cpp/README.md

@@ -21,10 +21,10 @@
 
 ## System setup
 
-Arrow uses CMake as a build configuration system. Currently, it supports in-source and
-out-of-source builds with the latter one being preferred.
+Arrow uses CMake as a build configuration system. Currently, it supports
+in-source and out-of-source builds with the latter one being preferred.
 
-Build Arrow requires:
+Building Arrow requires:
 
 * A C++11-enabled compiler. On Linux, gcc 4.8 and higher should be sufficient.
 * CMake
@@ -108,11 +108,11 @@ ASAN, and `ARROW_USE_ASAN` is mutually-exclusive with the valgrind option
 
 ### Building/Running fuzzers
 
-Fuzzers can help finding unhandled exceptions and problems with untrusted input that
-may lead to crashes, security issues and undefined behavior. They do this by
-generating random input data and observing the behavior of the executed code. To build
-the fuzzer code, LLVM is required (GCC-based compilers won't work). You can build them
-using the following code:
+Fuzzers can help finding unhandled exceptions and problems with untrusted input
+that may lead to crashes, security issues and undefined behavior. They do this
+by generating random input data and observing the behavior of the executed
+code. To build the fuzzer code, LLVM is required (GCC-based compilers won't
+work). You can build them using the following code:
 
     cmake -DARROW_FUZZING=ON -DARROW_USE_ASAN=ON ..
 
@@ -156,29 +156,18 @@ There are some problems that may occur during the compilation process:
 - libfuzzer was not distributed with your LLVM: `ld: file not found: .../libLLVMFuzzer.a`
 - your LLVM is too old: `clang: error: unsupported argument 'fuzzer' to option 'fsanitize='`
 
-### Third-party environment variables
-
-To set up your own specific build toolchain, here are the relevant environment
-variables
-
-* Boost: `BOOST_ROOT`
-* Googletest: `GTEST_HOME` (only required to build the unit tests)
-* gflags: `GFLAGS_HOME` (only required to build the unit tests)
-* Google Benchmark: `GBENCHMARK_HOME` (only required if building benchmarks)
-* Flatbuffers: `FLATBUFFERS_HOME` (only required for the IPC extensions)
-* Hadoop: `HADOOP_HOME` (only required for the HDFS I/O extensions)
-* jemalloc: `JEMALLOC_HOME`
-* brotli: `BROTLI_HOME`, can be disabled with `-DARROW_WITH_BROTLI=off`
-* lz4: `LZ4_HOME`, can be disabled with `-DARROW_WITH_LZ4=off`
-* snappy: `SNAPPY_HOME`, can be disabled with `-DARROW_WITH_SNAPPY=off`
-* zlib: `ZLIB_HOME`, can be disabled with `-DARROW_WITH_ZLIB=off`
-* zstd: `ZSTD_HOME`, can be disabled with `-DARROW_WITH_ZSTD=off`
-
-If you have all of your toolchain libraries installed at the same prefix, you
-can use the environment variable `$ARROW_BUILD_TOOLCHAIN` to automatically set
-all of these variables. Note that `ARROW_BUILD_TOOLCHAIN` will not set
-`BOOST_ROOT`, so if you have custom Boost installation, you must set this
-environment variable separately.
+### Third-party dependencies and configuration
+
+Arrow depends on a number of third-party libraries. We support these in a few
+ways:
+
+* Building dependencies from source by downloading archives from the internet
+* Building dependencies from source using from local archives (to allow offline
+  builds)
+* Building with locally-installed libraries
+
+See [thirdparty/README.md][5] for details about these options and how to
+configure your build toolchain.
 
 ### Building Python integration library (optional)
 
@@ -382,3 +371,4 @@ both of these options would be used rarely. Current known uses-cases when they a
 [2]: https://github.com/apache/arrow/blob/master/cpp/apidoc/Windows.md
 [3]: https://google.github.io/styleguide/cppguide.html
 [4]: https://github.com/include-what-you-use/include-what-you-use
+[5]: https://github.com/apache/arrow/blob/master/cpp/thirdparty/README.md