Failure in build_mac/build_thirdparty.sh - "CFLAGS: unbound variable" error

[sduzh]

After fixed #64775 I encountered another error while executing build_mac/build_thirdparty.sh:

./build_thirdparty.sh: line 1653: CFLAGS: unbound variable

Root Cause:

The issue appears to stem from the build_icu() function within build_thirdparty.sh, which unsets certain environment variables (including CFLAGS):

starrocks/build-mac/build_thirdparty.sh

Lines 1255 to 1257 in bc846fa

	unset CPPFLAGS
	unset CXXFLAGS
	unset CFLAGS