Work around gcc10 FAIL: S-records with constructors

gcc10 on x86_64 and powerpc64le recognises that the loop in
Foo::operator= can be turned into a call to memmove, which then
results in an undefined symbol when linking.  Avoid that by making the
loop smaller.

	* testsuite/ld-srec/sr3.cc (FOO_MSG_LEN): Set to 4.

ld/ChangeLog

@@ -1,3 +1,7 @@
+2019-09-22  Alan Modra  <amodra@gmail.com>
+
+	* testsuite/ld-srec/sr3.cc (FOO_MSG_LEN): Set to 4.
+
 2019-09-20  Nelson Chu <nelson.chu@sifive.com>
 
 	* testsuite/ld-riscv-elf/weakref32.s: Add relaxable undef weak code.

ld/testsuite/ld-srec/sr3.cc

@@ -1,6 +1,6 @@
 // This file is compiled and linked into the S-record format.
 
-#define FOO_MSG_LEN 80
+#define FOO_MSG_LEN 4
 
 class Foo {
     static int foos;