Merge pull request GafferHQ#5121 from johnhaddon/windowsBuildPR

Windows build fixes

.github/workflows/main/sconsOptions

@@ -63,5 +63,4 @@ if sys.platform == "win32" :
 	INKSCAPE = "C:\\Program Files\\Inkscape\\inkscape.com"
 	WARNINGS_AS_ERRORS = False
 	APPLESEED_ROOT = None
-	CXXFLAGS = "\"-DBOOST_ALL_NO_LIB\""
 	SPHINX = "noSphinxYet"

SConstruct

@@ -522,6 +522,7 @@ else:
 			"/DNOMINMAX",  # Suppress compiler definition of `min` and `max`
 			"/D__PRETTY_FUNCTION__=__FUNCSIG__",
 			"/DBOOST_ALL_DYN_LINK",
+			"/DBOOST_ALL_NO_LIB",
 			"/W4",  # Warning level 4, one level less than all warnings
 			"/experimental:external",  # Allow use of /external:I
 			"/external:W0",  # Suppress warnings for headers included with /external:I
@@ -790,8 +791,9 @@ if "BOOST_MAJOR_VERSION" not in baseLibEnv :
 
 basePythonEnv = baseLibEnv.Clone()
 
+pythonExecutable = shutil.which( "python", path = commandEnv["ENV"]["PATH"] )
 basePythonEnv["PYTHON_VERSION"] = subprocess.check_output(
-	[ "python", "-c", "import sys; print( '{}.{}'.format( *sys.version_info[:2] ) )" ],
+	[ pythonExecutable, "-c", "import sys; print( '{}.{}'.format( *sys.version_info[:2] ) )" ],
 	env=commandEnv["ENV"], universal_newlines=True
 ).strip()
 
@@ -800,7 +802,7 @@ if basePythonEnv["PLATFORM"] == "win32" :
 
 basePythonEnv["PYTHON_ABI_VERSION"] = basePythonEnv["PYTHON_VERSION"]
 basePythonEnv["PYTHON_ABI_VERSION"] += subprocess.check_output(
-	[ "python", "-c", "import sysconfig; print( sysconfig.get_config_var( 'abiflags' ) or '' )" ],
+	[ pythonExecutable, "-c", "import sysconfig; print( sysconfig.get_config_var( 'abiflags' ) or '' )" ],
 	env=commandEnv["ENV"], universal_newlines=True
 ).strip()