config/target: add float support selection

Changeset #149c33923f47 broke the architectures that do not
support the --with-float=X ./configure flag (in gcc). For example,
x86_64 does not support it.

Add a new blind config option that architectures can set to tell
they support floating point selection.

Reported-by: Morten Thunberg Svendsen <mts@doredevelopment.dk>
Signed-off-by: "Yann E. MORIN" <yann.morin.1998@anciens.enib.fr>

diff -dur strace-4.5.16.orig/system.c strace-4.5.16/system.c

--- strace-4.5.16.orig/system.c	2007-01-17 00:22:36.000000000 +0100

+++ strace-4.5.16/system.c	2007-07-14 19:28:41.000000000 +0200

@@ -1612,7 +1612,9 @@

 	{ CTL_KERN, "CTL_KERN" },

 	{ CTL_VM, "CTL_VM" },

 	{ CTL_NET, "CTL_NET" },

+#ifdef CTL_PROC

 	{ CTL_PROC, "CTL_PROC" },

+#endif

 	{ CTL_FS, "CTL_FS" },

 	{ CTL_DEBUG, "CTL_DEBUG" },

 	{ CTL_DEV, "CTL_DEV" },