As part of the initial changes for Issue13590 in 2.7.3, 3.2.3, and 3.3 (prior to release) to Distutils to support building extension modules on OS X with Xcode 4, code was added to substitute the clang compiler if the older gcc-4.2 supplied with Xcode 3 was not found.  In addition, the changes made it easier for the user to override the compiler for both the compile and linking stages: "Also as a convenience, if the user does explicitly set CC, substitute its value as the default compiler in the Distutils LDSHARED configuration variable for OS X."  This eliminated the need to construct a complete LDSHARED value.  For 2.7.4, 3.2.4, and 3.3.0, more extensive changes were made to fully support the latest releases of Xcode 4.  Unfortunately, the code to override LDSHARED if CC is set was inadvertently deleted for these later releases.  The attached patch restores the deleted override behavior and adds tests.