configury: explicitly disable gcc < v4.8.1

NOTE: The default GCC that ships in RHEL is v4.8.5.  Cisco regularly
tests GCC v4.8.1, and it works fine.  We know that PRTE and PMIX do
not compile with RHEL 6's default GCC (v4.4.7).  We know that v4.8.x
works and 4.4.7 doesn't, so set the lower bound support for 4.8.1.

Specifically: abort configure if the compiler is GCC and the version
is < v4.8.1.

Signed-off-by: Jeff Squyres <jsquyres@cisco.com>

Author: jsquyres

NEWS

@@ -77,6 +77,7 @@ Master (not on release branches yet)
 
 v5.0.0rc1 -- September, 2021
 --------------------
+
 - ORTE, the underlying OMPI launcher has been removed, and replaced
   with PRTE.
 - Reworked how Open MPI integrates with 3rd party packages.
@@ -94,6 +95,8 @@ v5.0.0rc1 -- September, 2021
 - Various ROMIO v3.4.1 updates.
 - Use Pandoc to generate manpages
 - 32 bit atomics are now only supported via C11 compliant compilers.
+- Explicitly disable support for GNU gcc < v4.8.1 (note: the default
+  gcc compiler that is included in RHEL 7 is v4.8.5).
 - Do not build Open SHMEM layer when there are no SPMLs available.
   Currently, this means the Open SHMEM layer will only build if
   the UCX library is found.

README.md

@@ -201,7 +201,7 @@ base as of this writing (April 2020):
 
 * On platforms other than x86-64, AArch64 (64-bit ARM), and PPC64,
   Open MPI requires a compiler that either supports C11 atomics or
-  the GCC `__atomic` atomics (e.g., GCC >= v4.7.2).
+  the GCC `__atomic` atomics (e.g., GCC >= v4.8.1).
 
 * 32-bit platforms are only supported with a recent compiler that
   supports C11 atomics. This includes gcc 4.9.x+ (gcc 6.x or newer

configure.ac

@@ -600,6 +600,22 @@ opal_show_subtitle "Compiler characteristics"
 OPAL_CHECK_ATTRIBUTES
 OPAL_CHECK_COMPILER_VERSION_ID
 
+# Open MPI only supports GCC >=v4.8.1.  Notes:
+#
+# 1. The default compiler that comes with RHEL 7 is v4.8.5 (version ID
+#    264197).
+# 2. We regularly test with GCC v4.8.1 (version ID 264193).
+# 3. GCC 4.8.0 probably also works; we just haven't tested it.
+#
+# Since we regularly test with 4.8.1, that's what we check for.
+AS_IF([test "$opal_cv_compiler_FAMILYNAME" = "GNU" && \
+       test "$opal_cv_compiler_VERSION" -lt 264193],
+      [AC_MSG_WARN([Open MPI no longer supports versions of the GNU compiler suite])
+       AC_MSG_WARN([less than v4.8.1.])
+       AC_MSG_WARN([Please upgrade your GNU compiler suite, or use])
+       AC_MSG_WARN([a different compiler to build Open MPI.])
+       AC_MSG_ERROR([Cannot continue])
+      ])
 
 ##################################
 # Java MPI Binding request