fix(build): Prevent sasl's makefile rules from staining vendor

Turns out Cyrus SASL doesn't use AM_MAINTAINER_MODE or anything to
prevent autotools from re-configuring the project at build time.
This patch "fixes" that by maiming autotools' paths in Makefile.

NO_DOC=internal
NO_TEST=internal
NO_CHANGELOG=internal

cmake/BuildSASL.cmake

@@ -12,6 +12,13 @@ macro(sasl_build)
     # Reusing approach from BuildLibCURL.cmake
     get_filename_component(OPENSSL_INSTALL_DIR ${OPENSSL_INCLUDE_DIR} DIRECTORY)
 
+    # NB: $(MAKE) will preserve jobserver in Makefiles.
+    if("${CMAKE_GENERATOR}" STREQUAL "Unix Makefiles")
+        set(MAKE_EXECUTABLE "$(MAKE)")
+    else()
+        set(MAKE_EXECUTABLE "make")
+    endif()
+
     include(ExternalProject)
     ExternalProject_Add(bundled-sasl
         DEPENDS OpenSSL::SSL OpenSSL::Crypto
@@ -43,6 +50,13 @@ macro(sasl_build)
 
             --disable-macos-framework
             --disable-sample
+
+        # HACK: prevent `am--refresh` rule from reconfiguring the project.
+        # Further reading: https://stackoverflow.com/a/5745366.
+        BUILD_COMMAND ${MAKE_EXECUTABLE}
+            AUTOCONF=: AUTOHEADER=: AUTOMAKE=: ACLOCAL=: all
+        INSTALL_COMMAND ${MAKE_EXECUTABLE}
+            AUTOCONF=: AUTOHEADER=: AUTOMAKE=: ACLOCAL=: install
     )
 
     unset(OPENSSL_INSTALL_DIR)