Merge bitcoin#12899: macOS: Prevent Xcode 9.3 build warnings

2eb5036 macOS: Prevent Xcode 9.3 build warnings (Akio Nakamura)

Pull request description:

  This PR intends to solve bitcoin#12867

  1. clang (Apple LLVM version 9.1.0 (clang-902.0.39.1)) warns unused argument '-pie' during compilation. This parameter should pass to the linker, so use '-Wl,-pie' style in configure.ac.
  2. The other hand, when linking libbitcoinconsensus.la with passing '-Wl,-pie', ld warns that '-pie' being ignored because not link a main executable. So remove it from $libbitcoinconsensus_la_LDFLAGS in src/Makefile.am.

  - In order to apply this change to Makefile, you need to run autogen.sh and ./configure.
  - I think no need to add if-clause by target-os because also g++ can recognize/handle  '-Wl,-pie'.
  - I confirmed that the build was successful on macos10.13.4/XCode9.3 and ubuntu 17.10/g++7.2.0 and that warning was not issued.

Tree-SHA512: 45b7c3881f3ad92172eb2ff6fa90c4dc70a42037450ea4b6fd87613b10c0aa90ebcffd54e7c50b70ba876b7c2e356825950fbf5a7a4e8e25118688d98d7b6ee0

Author: jonasschnelli

configure.ac

@@ -630,11 +630,7 @@ if test x$use_hardening != xno; then
   AX_CHECK_LINK_FLAG([[-Wl,--high-entropy-va]], [HARDENED_LDFLAGS="$HARDENED_LDFLAGS -Wl,--high-entropy-va"])
   AX_CHECK_LINK_FLAG([[-Wl,-z,relro]], [HARDENED_LDFLAGS="$HARDENED_LDFLAGS -Wl,-z,relro"])
   AX_CHECK_LINK_FLAG([[-Wl,-z,now]], [HARDENED_LDFLAGS="$HARDENED_LDFLAGS -Wl,-z,now"])
-
-  if test x$TARGET_OS != xwindows; then
-    AX_CHECK_COMPILE_FLAG([-fPIE],[PIE_FLAGS="-fPIE"])
-    AX_CHECK_LINK_FLAG([[-pie]], [HARDENED_LDFLAGS="$HARDENED_LDFLAGS -pie"])
-  fi
+  AX_CHECK_LINK_FLAG([[-fPIE -pie]], [PIE_FLAGS="-fPIE"; HARDENED_LDFLAGS="$HARDENED_LDFLAGS -pie"],, [[$CXXFLAG_WERROR]])
 
   case $host in
     *mingw*)