ci: convert PATH correctly to Cygwin format on Windows

We provide `BUILD_PATH` to our build script; provide it and mutate
`PATH` when running our tests as well.

We were previously using `cygpath` to try to convert a _list_ of Windows
paths into cygwin / Unix style `PATH` format. This does not work -- it
treats the path list as a single path (with semicolons -- understandably
as those are allowed characters in a Windows path).

For example, `C:\One;C:\Two;C:\Three` is converted to
`/c/one;c:/two;c:/three`.

Add a new function to convert path lists, so that paths are split by
semicolon and fed to `cygpath` independently, then re-joined with a
colon. This means that our example `C:\One;C:\Two;C:\Three` is correctly
converted to `/c/one:/c/two:/c/three`.

ci/build.sh

@@ -13,16 +13,30 @@ BUILD_PATH=${BUILD_PATH:=$PATH}
 CMAKE=$(which cmake)
 CMAKE_GENERATOR=${CMAKE_GENERATOR:-Unix Makefiles}
 
+indent() { sed "s/^/    /"; }
+
+cygfullpath() {
+	result=$(echo "${1}" | tr \; \\n | while read -r element; do
+		if [ "${last}" != "" ]; then echo -n ":"; fi
+		echo -n $(cygpath "${element}")
+		last="${element}"
+	done)
+	if [ "${result}" = "" ]; then exit 1; fi
+        echo "${result}"
+}
+
 if [[ "$(uname -s)" == MINGW* ]]; then
-	BUILD_PATH=$(cygpath "$BUILD_PATH")
+	BUILD_PATH=$(cygfullpath "${BUILD_PATH}")
 fi
 
-indent() { sed "s/^/    /"; }
 
 echo "Source directory: ${SOURCE_DIR}"
 echo "Build directory:  ${BUILD_DIR}"
 echo ""
 
+echo "Platform:"
+uname -s | indent
+
 if [ "$(uname -s)" = "Darwin" ]; then
 	echo "macOS version:"
 	sw_vers | indent
@@ -40,7 +54,7 @@ echo "Kernel version:"
 uname -a 2>&1 | indent
 
 echo "CMake version:"
-env PATH="${BUILD_PATH}" "${CMAKE}" --version 2>&1 | indent
+env PATH="${BUILD_PATH}" "${CMAKE}" --version | head -1 2>&1 | indent
 
 if test -n "${CC}"; then
 	echo "Compiler version:"

ci/test.sh

@@ -104,8 +104,18 @@ run_test() {
 
 indent() { sed "s/^/    /"; }
 
+cygfullpath() {
+	result=$(echo "${1}" | tr \; \\n | while read -r element; do
+		if [ "${last}" != "" ]; then echo -n ":"; fi
+		echo -n $(cygpath "${element}")
+		last="${element}"
+	done)
+	if [ "${result}" = "" ]; then exit 1; fi
+	echo "${result}"
+}
+
 if [[ "$(uname -s)" == MINGW* ]]; then
-        BUILD_PATH=$(cygpath "$BUILD_PATH")
+        BUILD_PATH=$(cygfullpath "$BUILD_PATH")
 fi