pw_toolchain: Make tools use relative paths

Changes GN toolchains to use relative paths to tools by default rather
than relying on the system PATH.

Bug: b/290848929
Change-Id: I580e39c14c32080c0448f9daf4d4f97801f9829f
Reviewed-on: https://pigweed-review.googlesource.com/c/pigweed/pigweed/+/159130
Presubmit-Verified: CQ Bot Account <pigweed-scoped@luci-project-accounts.iam.gserviceaccount.com>
Pigweed-Auto-Submit: Armando Montanez <amontanez@google.com>
Commit-Queue: Auto-Submit <auto-submit@pigweed-service-accounts.iam.gserviceaccount.com>
Reviewed-by: Alexei Frolov <frolv@google.com>

pw_toolchain/arm_gcc/toolchains.gni

@@ -16,10 +16,41 @@ import("//build_overrides/pigweed.gni")
 import("//build_overrides/pigweed_environment.gni")
 import("$dir_pw_toolchain/rbe.gni")
 
+_default_compiler_prefix = ""
+if (defined(pw_env_setup_CIPD_ARM)) {
+  _default_compiler_prefix = pw_env_setup_CIPD_ARM + "/bin/"
+}
+
+declare_args() {
+  # This flag allows you to specify the root directory of the ARM GCC tools to
+  # to use when compiling with an arm-none-eabi toolchain. This is useful for
+  # debugging toolchain-related issues, or for building with an
+  # externally-provided toolchain.
+  #
+  # If the prefix begins with "//", it will be rebased to be relative to the
+  # root build directory.
+  pw_toolchain_ARM_NONE_EABI_PREFIX = _default_compiler_prefix
+}
+
 # Specifies the tools used by ARM GCC toolchains.
 arm_gcc_toolchain_tools = {
   _rbe_debug_flag = ""
   _local_tool_name_root = "arm-none-eabi-"
+
+  _toolchain_prefix = pw_toolchain_ARM_NONE_EABI_PREFIX
+  if (_toolchain_prefix != "") {
+    # If the prefix is a GN-absolute path, rebase it so it's relative to the
+    # root of the build directory.
+    _split_prefix = string_split(_toolchain_prefix, "//")
+    if (_split_prefix[0] == "") {
+      _toolchain_prefix = rebase_path(_toolchain_prefix, root_build_dir)
+    }
+    _local_tool_name_root = _toolchain_prefix + _local_tool_name_root
+  }
+  if (host_os == "win") {
+    _local_tool_name_root = string_replace(_local_tool_name_root, "/", "\\")
+  }
+
   if (pw_toolchain_USE_RBE) {
     if (pw_toolchain_RBE_DEBUG) {
       _rbe_debug_flag = " -v "

pw_toolchain/clang_tools.gni

@@ -20,10 +20,16 @@ declare_args() {
   # and llvm-ar binaries to use when compiling with a clang-based toolchain.
   # This is useful for debugging toolchain-related issues by building with an
   # externally-provided toolchain.
-  pw_toolchain_CLANG_PREFIX = ""
+  #
+  # If the prefix begins with "//", it will be rebased to be relative to the
+  # root build directory.
+  pw_toolchain_CLANG_PREFIX = pw_env_setup_CIPD_PIGWEED + "/bin/"
 
   # This flag allows you to specify the root directory of the rustc binary.
-  pw_toolchain_RUST_PREFIX = ""
+  #
+  # If the prefix begins with "//", it will be rebased to be relative to the
+  # root build directory.
+  pw_toolchain_RUST_PREFIX = pw_env_setup_CIPD_PIGWEED + "/bin/"
 }
 
 pw_toolchain_clang_tools = {
@@ -33,15 +39,35 @@ pw_toolchain_clang_tools = {
   ld = cxx
   rustc = "rustc"
 
-  if (pw_toolchain_CLANG_PREFIX != "") {
-    ar = pw_toolchain_CLANG_PREFIX + ar
-    cc = pw_toolchain_CLANG_PREFIX + cc
-    cxx = pw_toolchain_CLANG_PREFIX + cxx
-    ld = pw_toolchain_CLANG_PREFIX + ld
+  _toolchain_prefix = pw_toolchain_CLANG_PREFIX
+  if (_toolchain_prefix != "") {
+    # If the prefix is a GN-absolute path, rebase it so it's relative to the
+    # root of the build directory.
+    _split_prefix = string_split(_toolchain_prefix, "//")
+    if (_split_prefix[0] == "") {
+      _toolchain_prefix = rebase_path(_toolchain_prefix, root_build_dir)
+    }
+    ar = _toolchain_prefix + ar
+    cc = _toolchain_prefix + cc
+    cxx = _toolchain_prefix + cxx
+    ld = _toolchain_prefix + ld
+  }
+  if (host_os == "win") {
+    _toolchain_prefix = string_replace(_toolchain_prefix, "/", "\\")
   }
 
-  if (pw_toolchain_RUST_PREFIX != "") {
-    rustc = pw_toolchain_RUST_PREFIX + rustc
+  _rust_prefix = pw_toolchain_RUST_PREFIX
+  if (host_os == "win") {
+    _rust_prefix = string_replace(_rust_prefix, "/", "\\")
+  }
+  if (_rust_prefix != "") {
+    # If the prefix is a GN-absolute path, rebase it so it's relative to the
+    # root of the build directory.
+    _split_rust_prefix = string_split(_rust_prefix, "//")
+    if (_split_rust_prefix[0] == "") {
+      _rust_prefix = rebase_path(_rust_prefix, root_build_dir)
+    }
+    rustc = _rust_prefix + rustc
   }
 
   if (pw_toolchain_USE_RBE) {