clover: Work around build failure with AltiVec.

Bugzilla: https://bugs.gentoo.org/show_bug.cgi?id=587210
Bugzilla: https://bugs.freedesktop.org/show_bug.cgi?id=68504
Acked-by: Francisco Jerez <currojerez@riseup.net>
(cherry picked from commit 7d1195c1e4)

configure.ac

@@ -2030,6 +2030,20 @@ if test "x$enable_opencl" = xyes; then
        AC_MSG_ERROR([Clover requires libelf])
     fi
 
+    if test "x${ac_cv_cxx_compiler_gnu}" = xyes; then
+        altivec_enabled=no
+        AC_COMPILE_IFELSE([AC_LANG_SOURCE([
+        #if !defined(__VEC__) || !defined(__ALTIVEC__)
+        #error "AltiVec not enabled"
+        #endif
+        ])], altivec_enabled=yes)
+
+        if test "$altivec_enabled" = yes; then
+            CLOVER_STD_OVERRIDE="-std=gnu++11"
+        fi
+        AC_SUBST([CLOVER_STD_OVERRIDE])
+    fi
+
     llvm_require_version $LLVM_REQUIRED_OPENCL "opencl"
 
     llvm_add_default_components "opencl"

src/gallium/state_trackers/clover/Makefile.am

@@ -33,6 +33,7 @@ noinst_LTLIBRARIES = libclover.la libcltgsi.la libclllvm.la
 
 libcltgsi_la_CXXFLAGS = \
 	-std=c++11 \
+	$(CLOVER_STD_OVERRIDE) \
 	$(VISIBILITY_CXXFLAGS)
 
 libcltgsi_la_SOURCES = $(TGSI_SOURCES)
@@ -41,6 +42,7 @@ libclllvm_la_CXXFLAGS = \
 	-std=c++11 \
 	$(VISIBILITY_CXXFLAGS) \
 	$(LLVM_CXXFLAGS) \
+	$(CLOVER_STD_OVERRIDE) \
 	$(DEFINES) \
 	$(LIBELF_CFLAGS) \
 	-DLIBCLC_INCLUDEDIR=\"$(LIBCLC_INCLUDEDIR)/\" \
@@ -51,6 +53,7 @@ libclllvm_la_SOURCES = $(LLVM_SOURCES)
 
 libclover_la_CXXFLAGS = \
 	-std=c++11 \
+	$(CLOVER_STD_OVERRIDE) \
 	$(VISIBILITY_CXXFLAGS)
 
 libclover_la_LIBADD = \