powerpc64le: blacklist broken GCC compilers (e.g GCC 7.5.0)

GCC 7.5.0 (PR94200) will refuse to compile if both -mabi=% and
-mlong-double-128 are passed on the command line.  Surprisingly,
it will work happily if the latter is not.  For the sake of
maintaining status quo, test for and blacklist such compilers.

Tested with a GCC 8.3.1 and GCC 7.5.0 compiler for ppc64le.

Reviewed-by: Tulio Magno Quites Machado Filho <tuliom@linux.ibm.com>

1 files changed, 8 insertions, 2 deletions

diff --git a/manual/install.texi b/manual/install.texi
index e801abd8be..f6d9d92317 100644
--- a/manual/install.texi
+++ b/manual/install.texi
@@ -509,8 +509,14 @@ release time, GCC 9.2.1 is the newest compiler verified to work to build
 
 For PowerPC 64-bits little-endian (powerpc64le), a GCC version with support
 for @option{-mno-gnu-attribute}, @option{-mabi=ieeelongdouble}, and
-@option{-mabi=ibmlondouble} is required.  These additional features are
-required for building the GNU C Library with support for IEEE long double.
+@option{-mabi=ibmlondouble} is required.  Likewise, the compiler must also
+support passing @option{-mlong-double-128} with the preceding options.  As
+of release, this implies GCC 7.4 and newer (excepting GCC 7.5.0, see GCC
+PR94200).  These additional features are required for building the GNU C
+Library with support for IEEE long double.
+
+@c powerpc64le performs an autoconf test to verify the compiler compiles with
+@c commands like "$CC -c foo.c -mabi=ibmlongdouble -mlong-double-128".
 
 For multi-arch support it is recommended to use a GCC which has been built with
 support for GNU indirect functions.  This ensures that correct debugging