Index: config/gnu-cxxflags
--- config/gnu-cxxflags.orig	2019-10-18 15:38:05.000000000 +0200
+++ config/gnu-cxxflags	2019-12-24 09:36:11.617210000 +0100
@@ -92,10 +92,10 @@
     esac
 
     # General (copied from H5_CFLAGS)
-    H5_CXXFLAGS="$H5_CXXFLAGS $arch -pedantic -Wall -W -Wundef -Wshadow -Wpointer-arith -Wcast-qual -Wcast-align -Wwrite-strings -Wconversion -Wredundant-decls -Winline"
+    H5_CXXFLAGS="$H5_CXXFLAGS $arch"
 
     # C++-specific
-    H5_CXXFLAGS="$H5_CXXFLAGS -Wsign-promo -Woverloaded-virtual -Wold-style-cast -Weffc++ -Wreorder -Wnon-virtual-dtor -Wctor-dtor-privacy -Wabi"
+    H5_CXXFLAGS="$H5_CXXFLAGS"
 
     # Production
     # NDEBUG is handled explicitly by the configure script
Index: config/gnu-flags
--- config/gnu-flags.orig	2019-12-24 09:36:11.617390000 +0100
+++ config/gnu-flags	2019-12-24 09:37:45.283894000 +0100
@@ -168,12 +168,6 @@
     # NOTE: Disable the -Wformat-nonliteral from -Wformat=2 here and re-add
     # it to the developer flags.
     #
-    H5_CFLAGS="$H5_CFLAGS -pedantic -Wall -Wextra -Wbad-function-cast -Wc++-compat -Wcast-align"
-    H5_CFLAGS="$H5_CFLAGS -Wcast-qual -Wconversion -Wdeclaration-after-statement -Wdisabled-optimization -Wfloat-equal"
-    H5_CFLAGS="$H5_CFLAGS -Wformat=2 -Wno-format-nonliteral -Winit-self -Winvalid-pch -Wmissing-declarations -Wmissing-include-dirs"
-    H5_CFLAGS="$H5_CFLAGS -Wmissing-prototypes -Wnested-externs -Wold-style-definition -Wpacked"
-    H5_CFLAGS="$H5_CFLAGS -Wredundant-decls -Wshadow -Wstrict-prototypes -Wswitch-enum -Wswitch-default"
-    H5_CFLAGS="$H5_CFLAGS -Wundef -Wunused-macros -Wunsafe-loop-optimizations -Wwrite-strings"
 
     ######################
     # Developer warnings #
Index: java/test/h5ex_g_iterate
Index: src/H5FDdirect.c
--- src/H5FDdirect.c.orig	2019-12-19 17:38:30.000000000 +0100
+++ src/H5FDdirect.c	2019-12-24 09:36:11.617689000 +0100
@@ -484,7 +484,9 @@
     if (H5F_ACC_EXCL & flags) o_flags |= O_EXCL;
 
     /* Flag for Direct I/O */
+#ifdef O_DIRECT
     o_flags |= O_DIRECT;
+#endif
 
     /* Open the file */
     if ((fd = HDopen(name, o_flags, H5_POSIX_CREATE_MODE_RW))<0)