[Build] Add compile/link summary to configure

[Fuzzbawls]

This adds a summary of compiler and linker flags, as well as information
about which features are enabled/disabled to the end of the configure
script.

Doesn't change any functionality, and is strictly informational.

Example Output:

Options used to compile and link:
  with wallet   = yes
  with gui / qt = yes
    qt version  = 5
    with qr     = yes
  with zmq      = yes
  with test     = yes
  with upnp     = yes
  debug enabled = no

  target os     = darwin
  build os      = darwin

  CC            = /usr/local/bin/ccache gcc
  CFLAGS        = -g -O2
  CPPFLAGS      = -Qunused-arguments -I/usr/local/opt/openssl/include -DBOOST_SPIRIT_THREADSAFE -DHAVE_BUILD_INFO -D__STDC_FORMAT_MACROS -I/usr/local/opt/berkeley-db@4/include -DMAC_OSX  -U_FORTIFY_SOURCE -D_FORTIFY_SOURCE=2 -DHAVE_QT5
  CXX           = /usr/local/bin/ccache g++ -std=c++11
  CXXFLAGS      = -g -O2 -Wall -Wextra -Wformat -Wformat-security -Wno-unused-parameter  -Wstack-protector -fstack-protector-all -fPIC -fvisibility=hidden
  LDFLAGS       = -L/usr/local/opt/openssl/lib -Wl,-headerpad_max_install_names  -Wl,-dead_strip

[PIVX-Project]

utACK

[rejectedpromise]

utACK

[jonspock]

Tested ACK, will merge