* and #pragma pop_macro("macro_name")

* give warning if pragma is unknown for tcc
    * don't free asm_label in sym_free(),
      it's a job of the asm_free_labels().

    The above pragmas are used in the mingw headers.
    Thise pragmas are implemented in gcc-4.5+ and current
    clang.

tests/tests2/77_push_pop_macro.c

@@ -0,0 +1,23 @@
+#include <stdio.h>
+
+int main()
+{
+    #define abort "111"
+    printf("abort = %s\n", abort);
+
+    #pragma push_macro("abort")
+    #undef abort
+    #define abort "222"
+    printf("abort = %s\n", abort);
+
+    #pragma push_macro("abort")
+    #undef abort
+    #define abort "333"
+    printf("abort = %s\n", abort);
+
+    #pragma pop_macro("abort")
+    printf("abort = %s\n", abort);
+
+    #pragma pop_macro("abort")
+    printf("abort = %s\n", abort);
+}

tests/tests2/77_push_pop_macro.expect

@@ -0,0 +1,5 @@
+abort = 111
+abort = 222
+abort = 333
+abort = 222
+abort = 111

tests/tests2/Makefile

@@ -95,7 +95,8 @@ TESTS =	\
  73_arm64.test \
  74_nocode_wanted.test \
  75_array_in_struct_init.test \
- 76_dollars_in_identifiers.test
+ 76_dollars_in_identifiers.test \
+ 77_push_pop_macro.test
 
 # 34_array_assignment.test -- array assignment is not in C standard