Quote $CC in library_check.sh

This commit fixes failure-to-build on systems where the path to the
compiler contains spaces. This is common on Microsoft Windows, where the
compiler lives somewhere under `C:\Program Files`. Prior to this commit,
src/ansi-c/library_check.sh would try to execute `C:\Program` and fail.

Author: karkhaz

src/ansi-c/library_check.sh

@@ -10,8 +10,8 @@ for f in "$@"; do
     perl -p -i -e 's/(_mm_.fence)/s$1/' __libcheck.c
     perl -p -i -e 's/(__sync_)/s$1/' __libcheck.c
     perl -p -i -e 's/(__noop)/s$1/' __libcheck.c
-    $CC -std=gnu99 -E -include library/cprover.h -D__CPROVER_bool=_Bool -D__CPROVER_thread_local=__thread -DLIBRARY_CHECK -o __libcheck.i __libcheck.c
-    $CC -S -Wall -Werror -pedantic -Wextra -std=gnu99 __libcheck.i -o __libcheck.s -Wno-unused-label
+    "$CC" -std=gnu99 -E -include library/cprover.h -D__CPROVER_bool=_Bool -D__CPROVER_thread_local=__thread -DLIBRARY_CHECK -o __libcheck.i __libcheck.c
+    "$CC" -S -Wall -Werror -pedantic -Wextra -std=gnu99 __libcheck.i -o __libcheck.s -Wno-unused-label
     ec="${?}"
     rm __libcheck.s __libcheck.i __libcheck.c
     [ "${ec}" -eq 0 ] || exit "${ec}"