build: consistently quote arguments in AC_ARG_VAR()

build-aux/m4/bitcoin_find_bdb48.m4

@@ -3,8 +3,8 @@ dnl Distributed under the MIT software license, see the accompanying
 dnl file COPYING or http://www.opensource.org/licenses/mit-license.php.
 
 AC_DEFUN([BITCOIN_FIND_BDB48],[
-  AC_ARG_VAR(BDB_CFLAGS, [C compiler flags for BerkeleyDB, bypasses autodetection])
-  AC_ARG_VAR(BDB_LIBS, [Linker flags for BerkeleyDB, bypasses autodetection])
+  AC_ARG_VAR([BDB_CFLAGS], [C compiler flags for BerkeleyDB, bypasses autodetection])
+  AC_ARG_VAR([BDB_LIBS], [Linker flags for BerkeleyDB, bypasses autodetection])
 
   if test "x$use_bdb" = "xno"; then
     use_bdb=no

configure.ac

@@ -30,7 +30,7 @@ BITCOIN_MP_NODE_NAME=bitcoin-node
 BITCOIN_MP_GUI_NAME=bitcoin-gui
 
 dnl Unless the user specified ARFLAGS, force it to be cr
-AC_ARG_VAR(ARFLAGS, [Flags for the archiver, defaults to <cr> if not set])
+AC_ARG_VAR([ARFLAGS], [Flags for the archiver, defaults to <cr> if not set])
 if test "x${ARFLAGS+set}" != "xset"; then
   ARFLAGS="cr"
 fi
@@ -117,7 +117,7 @@ AC_PATH_TOOL([OBJCOPY], [objcopy])
 AC_PATH_PROG([DOXYGEN], [doxygen])
 AM_CONDITIONAL([HAVE_DOXYGEN], [test -n "$DOXYGEN"])
 
-AC_ARG_VAR(PYTHONPATH, Augments the default search path for python module files)
+AC_ARG_VAR([PYTHONPATH], [Augments the default search path for python module files])
 
 AC_ARG_ENABLE([wallet],
   [AS_HELP_STRING([--disable-wallet],