[build-windows] Remove hard-coded C:

.. and use `%SystemDrive%` instead to enhance robustness.

Author: stevapple

utils/build-windows.bat

@@ -83,7 +83,7 @@ call :build_swift %exitOnError%
 
 call :build_lldb %exitOnError%
 
-path %PATH%;C:\Program Files\Git\usr\bin
+path %PATH%;%SystemDrive%\Program Files\Git\usr\bin
 call :build_libdispatch %exitOnError%
 
 path %install_directory%\bin;%build_root%\swift\bin;%build_root%\swift\libdispatch-prefix\bin;%PATH%
@@ -142,7 +142,7 @@ set file_name=icu4c-%icu_version%-Win64-MSVC2017.zip
 curl -L -O "https://github.com/unicode-org/icu/releases/download/release-%icu_version_dashed%/%file_name%" %exitOnError%
 :: unzip warns about the paths in the zip using slashes, which raises the
 :: errorLevel to 1. We cannot use exitOnError, and have to ignore errors.
-"C:\Program Files\Git\usr\bin\unzip.exe" -o %file_name% -d "%source_root%\icu-%icu_version%"
+"%SystemDrive%\Program Files\Git\usr\bin\unzip.exe" -o %file_name% -d "%source_root%\icu-%icu_version%"
 exit /b 0
 
 goto :eof
@@ -156,7 +156,7 @@ setlocal enableextensions enabledelayedexpansion
 
 set file_name=sqlite-amalgamation-3270200.zip
 curl -L -O "https://www.sqlite.org/2019/%file_name%" %exitOnError%
-"C:\Program Files\Git\usr\bin\unzip.exe" -o %file_name% %exitOnError%
+"%SystemDrive%\Program Files\Git\usr\bin\unzip.exe" -o %file_name% %exitOnError%
 
 goto :eof
 endlocal