Fix math feature tests when compiling with tcc (re: 92f7ca54) (#303)

Commit 92f7ca54 broke compilation with tcc on Linux. The following
error would occur while compiling ksh with tcc:

  In file included from /home/johno/GitRepos/KornShell/ksh/src/cmd/ksh93/data/strdata.c:105:
  ./FEATURE/math:91: error: too many basic types
  mamake [cmd/ksh93]: *** exit code 1 making strdata.o

The build failure is fixed by backporting the relevant bugfix from
the 93v- version of iffe.

src/cmd/INIT/iffe.sh:
- Backport the 2013 iffe bugfix for the intrinsic function test to
  rule out type names (dated 2013-08-11 in the 93v- changelog).

src/cmd/INIT/iffe.sh

@@ -4066,6 +4066,9 @@ $std
 $usr
 $pre
 $inc
+#ifdef _IFFE_type
+$v i;
+#else
 typedef int (*_IFFE_fun)();
 #ifdef _IFFE_extern
 _BEGIN_EXTERNS_
@@ -4073,6 +4076,7 @@ extern int $v();
 _END_EXTERNS_
 #endif
 static _IFFE_fun i=(_IFFE_fun)$v;int main(){return ((unsigned int)i)^0xaaaa;}
+#endif
 "
 					d=-D_IFFE_extern
 					if	compile $cc -c $tmp.c <&$nullin >&$nullout
@@ -4100,6 +4104,8 @@ static _IFFE_fun i=(_IFFE_fun)$v;int main(){return ((unsigned int)i)^0xaaaa;}
 								;;
 							esac
 						fi
+					else	if	compile $cc -D_IFFE_type -c $tmp.c <&$nullin >&$nullout
+						then	c=1
 						else	case $intrinsic in
 							'')	copy $tmp.c "
 $tst
@@ -4117,9 +4123,11 @@ static int ((*i)())=foo;int main(){return(i==0);}
 								intrinsic=$?
 								;;
 							esac
+							c=$intrinsic
+						fi
 						case $o in
-						mth)	report $intrinsic 1 "$v() in math lib" "$v() not in math lib" "default for function $v()" ;;
+						mth)	report $c 1 "$v() in math lib" "$v() not in math lib" "default for function $v()" ;;
-						*)	report $intrinsic 1 "$v() in default lib(s)" "$v() not in default lib(s)" "default for function $v()" ;;
+						*)	report $c 1 "$v() in default lib(s)" "$v() not in default lib(s)" "default for function $v()" ;;
 						esac
 					fi
 					;;