Ignore unknown pragmas

Since new compilers has new checks (like -Wdangling-pointer), and so to
avoid extra checks in cmake/autotools, simply suppress if the pragma is
unknown.

CMakeLists.txt

@@ -317,6 +317,8 @@ if (${GNUC})
 
          # Disable unused-function warnings. These trigger for minheap-internal.h.
          -Wno-unused-function
+
+         -Wno-pragmas
     )
 
     if (${CLANG})

configure.ac

@@ -772,6 +772,9 @@ if test "$enable_gcc_warnings" != "no" && test "$GCC" = "yes"; then
    dnl Disable unused-function warnings. These trigger for minheap-internal.h.
    AX_CHECK_COMPILE_FLAG([-Wno-unused-function], [CFLAGS="$CFLAGS -Wno-unused-function"],[],[-Werror])
 
+   dnl Disable unknown pragmas warnings.
+   AX_CHECK_COMPILE_FLAG([-Wno-pragmas], [CFLAGS="$CFLAGS -Wno-pragmas"],[],[-Werror])
+
   if test "$have_clang" = "yes"; then
     case "$host_os" in
       darwin*)