build_instructions.md: Document Windows Build. Add approximate GCC,…

… Clang versions.

  - Add approximate required versions of GCC/Clang.
    - Address #4, but leave issue open until we enforce this in the build.
  - Adds some documentation on how to build for native Windows, and we have existing GitHub CI building it. Close some issues:
    - Fix #5
    - Fix #6.
    - Due to bazelbuild/bazel#22763 it is difficult to configure custom "startup" options for windows. For now the instructions tell the user what configuration changes can be used to fix Windows "long path issues".
  - Drop "Linux" from build instructions header. All platform specific requirements are in the prerequisite sections. Build and test commands work on all supported platforms.

PiperOrigin-RevId: 688994914

docs/build_instructions.md

@@ -2,13 +2,32 @@
 
 ## Prerequisites for building the encoder
 
+### All platforms
+
 -   Bazel: `iamf-tools` uses the Bazel build system. See Bazel's
     [Getting started](https://bazel.build/start) page for installation
     instructions.
 -   CMake: required to build some dependencies. See CMake's
     [Download](https://cmake.org/download/) page to install.
+-   Clang 13+ or GCC 10+ for Linux-like systems or MSVC for Windows.
+
+### Additional Windows prerequisites
+
+Windows requires some additional prerequisites:
+
+-   MSYS32: See [msys2.org](https://www.msys2.org/) for installation
+    instructions.
+-   MSCV: Follow Bazel's
+    [Build on Windows](https://bazel.build/configure/windows) for installation
+    instructions.
+-   Address
+    [long path issues](https://bazel.build/configure/windows#long-path-issues)
+    by adding the following to `iamf-tools/.bazelrc` or another
+    [custom .bazelrc](https://bazel.build/run/bazelrc) file:
 
-## Building the encoder on Linux
+    `startup --output_user_root=C:/tmp`
+
+## Building the encoder
 
 Building the encoder binary:
 
@@ -24,9 +43,10 @@ bazel test -c opt //iamf/...
 
 ## Test suite
 
-[iamf/cli/testdata](../iamf/cli/testdata) covers a wide variety of IAMF features.
-These samples can be used as encoder input. After encoding the resultant `.iamf`
-files can be used to assist in testing or debugging an IAMF-compliant decoder.
+[iamf/cli/testdata](../iamf/cli/testdata) covers a wide variety of IAMF
+features. These samples can be used as encoder input. After encoding the
+resultant `.iamf` files can be used to assist in testing or debugging an
+IAMF-compliant decoder.
 
 See the separate [README.md](../iamf/cli/testdata/README.md) for further
 documentation.
@@ -63,4 +83,6 @@ documentation.
 *   `docs/` - Documentation.
 
 ## Contributing
-If you have improvements or fixes, we would love to have your contributions. See [CONTRIBUTING.md](../CONTRIBUTING.md) for details.
+
+If you have improvements or fixes, we would love to have your contributions. See
+[CONTRIBUTING.md](../CONTRIBUTING.md) for details.