build: remove glibc-back-compat from build system

At this point, or minimum required glibc is implicitly 2.18, due to
thread_local support being enabled by default. However, users can
disable thread_local support to maintain 2.17 ccompat for now, which is
currently done in the Guix build.

configure.ac

@@ -240,15 +240,9 @@ AC_ARG_ENABLE([lcov-branch-coverage],
   [use_lcov_branch=yes],
   [use_lcov_branch=no])
 
-AC_ARG_ENABLE([glibc-back-compat],
-  [AS_HELP_STRING([--enable-glibc-back-compat],
-  [enable backwards compatibility with glibc])],
-  [use_glibc_compat=$enableval],
-  [use_glibc_compat=no])
-
 AC_ARG_ENABLE([threadlocal],
   [AS_HELP_STRING([--enable-threadlocal],
-  [enable features that depend on the c++ thread_local keyword (currently just thread names in debug logs). (default is to enabled if there is platform support and glibc-back-compat is not enabled)])],
+  [enable features that depend on the c++ thread_local keyword (currently just thread names in debug logs). (default is to enable if there is platform support)])],
   [use_thread_local=$enableval],
   [use_thread_local=auto])
 
@@ -863,17 +857,7 @@ if test x$ac_cv_sys_large_files != x &&
   CPPFLAGS="$CPPFLAGS -D_LARGE_FILES=$ac_cv_sys_large_files"
 fi
 
-if test x$use_glibc_compat != xno; then
-  AX_CHECK_LINK_FLAG([[-Wl,--wrap=__divmoddi4]], [COMPAT_LDFLAGS="$COMPAT_LDFLAGS -Wl,--wrap=__divmoddi4"])
-  AX_CHECK_LINK_FLAG([[-Wl,--wrap=log2f]], [COMPAT_LDFLAGS="$COMPAT_LDFLAGS -Wl,--wrap=log2f"])
-  case $host in
-    powerpc64* | ppc64*)
-      AX_CHECK_LINK_FLAG([[-Wl,--no-tls-get-addr-optimize]], [COMPAT_LDFLAGS="$COMPAT_LDFLAGS -Wl,--no-tls-get-addr-optimize"])
-    ;;
-  esac
-else
-  AC_SEARCH_LIBS([clock_gettime],[rt])
-fi
+AC_SEARCH_LIBS([clock_gettime],[rt])
 
 if test "x$enable_gprof" = xyes; then
     dnl -pg is incompatible with -pie. Since hardening and profiling together doesn't make sense,
@@ -1065,7 +1049,7 @@ AC_COMPILE_IFELSE([AC_LANG_SOURCE([
 dnl thread_local is currently disabled when building with glibc back compat.
 dnl Our minimum supported glibc is 2.17, however support for thread_local
 dnl did not arrive in glibc until 2.18.
-if test "x$use_thread_local" = xyes || { test "x$use_thread_local" = xauto && test "x$use_glibc_compat" = xno; }; then
+if test "x$use_thread_local" = xyes || test "x$use_thread_local" = xauto; then
   TEMP_LDFLAGS="$LDFLAGS"
   LDFLAGS="$TEMP_LDFLAGS $PTHREAD_CFLAGS"
   AC_MSG_CHECKING([for thread_local support])
@@ -1806,7 +1790,6 @@ AM_CONDITIONAL([ENABLE_BENCH],[test x$use_bench = xyes])
 AM_CONDITIONAL([USE_QRCODE], [test x$use_qr = xyes])
 AM_CONDITIONAL([USE_LCOV],[test x$use_lcov = xyes])
 AM_CONDITIONAL([USE_LIBEVENT],[test x$use_libevent = xyes])
-AM_CONDITIONAL([GLIBC_BACK_COMPAT],[test x$use_glibc_compat = xyes])
 AM_CONDITIONAL([HARDEN],[test x$use_hardening = xyes])
 AM_CONDITIONAL([ENABLE_SSE42],[test x$enable_sse42 = xyes])
 AM_CONDITIONAL([ENABLE_SSE41],[test x$enable_sse41 = xyes])
@@ -1849,7 +1832,6 @@ AC_SUBST(DEBUG_CPPFLAGS)
 AC_SUBST(WARN_CXXFLAGS)
 AC_SUBST(NOWARN_CXXFLAGS)
 AC_SUBST(DEBUG_CXXFLAGS)
-AC_SUBST(COMPAT_LDFLAGS)
 AC_SUBST(ERROR_CXXFLAGS)
 AC_SUBST(GPROF_CXXFLAGS)
 AC_SUBST(GPROF_LDFLAGS)

src/Makefile.am

@@ -571,7 +571,7 @@ libbitcoin_common_a_SOURCES = \
 
 # util: shared between all executables.
 # This library *must* be included to make sure that the glibc
-# backward-compatibility objects and their sanity checks are linked.
+# sanity checks are linked.
 libbitcoin_util_a_CPPFLAGS = $(AM_CPPFLAGS) $(BITCOIN_INCLUDES)
 libbitcoin_util_a_CXXFLAGS = $(AM_CXXFLAGS) $(PIE_FLAGS)
 libbitcoin_util_a_SOURCES = \
@@ -619,11 +619,6 @@ if USE_LIBEVENT
 libbitcoin_util_a_SOURCES += util/url.cpp
 endif
 
-if GLIBC_BACK_COMPAT
-libbitcoin_util_a_SOURCES += compat/glibc_compat.cpp
-AM_LDFLAGS += $(COMPAT_LDFLAGS)
-endif
-
 # cli: shared between bitcoin-cli and bitcoin-qt
 libbitcoin_cli_a_CPPFLAGS = $(AM_CPPFLAGS) $(BITCOIN_INCLUDES)
 libbitcoin_cli_a_CXXFLAGS = $(AM_CXXFLAGS) $(PIE_FLAGS)
@@ -751,10 +746,6 @@ if BUILD_BITCOIN_LIBS
 include_HEADERS = script/bitcoinconsensus.h
 libbitcoinconsensus_la_SOURCES = support/cleanse.cpp $(crypto_libbitcoin_crypto_base_a_SOURCES) $(libbitcoin_consensus_a_SOURCES)
 
-if GLIBC_BACK_COMPAT
-  libbitcoinconsensus_la_SOURCES += compat/glibc_compat.cpp
-endif
-
 libbitcoinconsensus_la_LDFLAGS = $(AM_LDFLAGS) -no-undefined $(RELDFLAGS)
 libbitcoinconsensus_la_LIBADD = $(LIBSECP256K1)
 libbitcoinconsensus_la_CPPFLAGS = $(AM_CPPFLAGS) -I$(builddir)/obj -I$(srcdir)/secp256k1/include -DBUILD_BITCOIN_INTERNAL