[Darwin, PPC, committed] Do not use longcall for 64b code.

[Iain Sandoe]

The linker [ld64] that supports 64Bit does not need the JBSR longcall
optimisation, and will not work with the most generic case (where the
symbol is undefined external, but there is no symbl stub).  So switch
the longcall option off.  ld64 will generate branch islands as needed.

tested on powerpc-darwin9.
applied to mainline
thanks
Iain

2019-06-27  Iain Sandoe  <i...@sandoe.co.uk>

        * config/rs6000/rs6000.c (darwin_rs6000_override_options): Do not
        use longcall for 64b code.

diff --git a/gcc/config/rs6000/rs6000.c b/gcc/config/rs6000/rs6000.c
index 3b59db5..fbff6bd 100644
--- a/gcc/config/rs6000/rs6000.c
+++ b/gcc/config/rs6000/rs6000.c
@@ -3418,6 +3418,15 @@ darwin_rs6000_override_options (void)
       rs6000_isa_flags |= OPTION_MASK_POWERPC64;
       warning (0, "%qs requires PowerPC64 architecture, enabling", "-m64");
     }
+
+  /* The linkers [ld64] that support 64Bit do not need the JBSR longcall
+     optimisation, and will not work with the most generic case (where the
+     symbol is undefined external, but there is no symbl stub).  */
+  if (TARGET_64BIT)
+    rs6000_default_long_calls = 0;
+
+  /* ld_classic is (so far) still used for kernel (static) code, and supports
+     the JBSR longcall / branch islands.  */
   if (flag_mkernel)
     {
       rs6000_default_long_calls = 1;