Bazel bootstrapping: make it work on Windows again

In this change:

(1) add a sanity check to verify that GNU bintools
are on the PATH

(2) correct the PATH on Windows if (1) failed

(3) use "<user>/My Documents/Temp" as the default
temp directory instead of "%windir%/Temp", because
the latter is non-writable

Motivated by:
https://github.com/bazelbuild/bazel/issues/2431
https://github.com/bazelbuild/bazel/issues/2449

--
PiperOrigin-RevId: 146006796
MOS_MIGRATED_REVID=146006796

compile.sh

diff --git a/compile.sh b/compile.sh
index dfc3d71..67223e6 100755
--- a/compile.sh
+++ b/compile.sh
@@ -22,6 +22,26 @@
 
 set -o errexit
 
+# Correct PATH on Windows, to avoid using "FIND.EXE" instead of "/usr/bin/find"
+# etc, leading to confusing errors.
+export BAZEL_OLD_PATH=$PATH
+case "$(uname -s | tr [:upper:] [:lower:])" in
+msys*|mingw*)
+  # Check that the PATH is set up correctly by attempting to locate `[`.
+  # This ensures that `which` is installed correctly and can succeed, while
+  # also avoids accidentally locating a tool that exists in plain Windows too
+  # (like "find" for "FIND.EXE").
+  which [ >&/dev/null || export PATH="/bin:/usr/bin:$PATH"
+esac
+
+# Check that the bintools can be found, otherwise we would see very confusing
+# error messages.
+which [ >&/dev/null || {
+  echo >&2 "ERROR: cannot locate GNU bintools; check your PATH."
+  echo >&2 "       (You may need to run 'export PATH=/bin:/usr/bin:\$PATH)'"
+  exit 1
+}
+
 cd "$(dirname "$0")"
 
 # Set the default verbose mode in buildenv.sh so that we do not display command

scripts/bootstrap/buildenv.sh

diff --git a/scripts/bootstrap/buildenv.sh b/scripts/bootstrap/buildenv.sh
index 502f2c1..60a375d 100755
--- a/scripts/bootstrap/buildenv.sh
+++ b/scripts/bootstrap/buildenv.sh
@@ -84,20 +84,15 @@
   JAVA_HOME="${JAVA_HOME:-$(ls -d /c/Program\ Files/Java/jdk* | sort | tail -n 1)}"
 esac
 
-# Extension for executables.
 EXE_EXT=""
-case "${PLATFORM}" in
-msys*|mingw*)
+if [ "${PLATFORM}" == "mingw" ]; then
+  # Extension for executables.
   EXE_EXT=".exe"
-esac
 
-# Fix TMPDIR on msys
-case "${PLATFORM}" in
-msys*|mingw*)
-  default_tmp=${TMP:-$(cygpath -W)/Temp}
+  # Fix TMPDIR on msys
+  default_tmp=${TMP:-$(cygpath -mO)/Temp}
   TMPDIR=$(cygpath -ml "${TMPDIR:-$default_tmp}")
-esac
-
+fi
 
 # Whether we display build messages or not.  We set this conditionally because
 # the file including us or the user may already have defined VERBOSE to their
@@ -118,6 +113,11 @@
   ATEXIT_HANDLERS="${ATEXIT_HANDLERS} ${handler}"
 }
 
+function restore_saved_path() {
+  export PATH=$BAZEL_OLD_PATH
+  export BAZEL_OLD_PATH=
+}
+
 # Exit routine to run all registered atexit handlers.
 #
 # If the program exited with an error, this exit routine will also exit with the
@@ -146,6 +146,7 @@
 
 function tempdir() {
   local tmp=${TMPDIR:-/tmp}
+  mkdir -p ${tmp}
   local DIR="$(mktemp -d ${tmp%%/}/bazel_XXXXXXXX)"
   mkdir -p "${DIR}"
   local DIRBASE=$(basename "${DIR}")
@@ -164,6 +165,7 @@
 }
 
 atexit cleanup_phasefile
+atexit restore_saved_path
 
 # Excutes a command respecting the current verbosity settings.
 #