testsuite: [arm] Add arm_softfp_ok and arm_hard_ok effective targets.

For arm-linux-gnueabi* targets, a toolchain cannot support the
float-abi opposite to the one it has been configured for: since glibc
does not support such multilibs, we end up lacking gnu/stubs-*.h when
including stdint.h for instance.

This patch introduces two new effective targets to detect whether we
can compile tests with -mfloat-abi=softfp or -mfloat-abi=hard.

This enables to make such tests unsupported rather than fail.

2020-04-22  Christophe Lyon  <christophe.lyon@linaro.org>

	gcc/testsuite/
	* lib/target-supports.exp (arm_softfp_ok): New effective target.
	(arm_hard_ok): Likewise.

	gcc/
	* doc/sourcebuild.texi (arm_softfp_ok, arm_hard_ok): Document.

gcc/ChangeLog

+2020-04-22  Christophe Lyon  <christophe.lyon@linaro.org>
+
+	* doc/sourcebuild.texi (arm_softfp_ok, arm_hard_ok): Document.
+
 2020-04-22  Kyrylo Tkachov  <kyrylo.tkachov@arm.com>
             Andre Vieira  <andre.simoesdiasvieira@arm.com>
             Mihail Ionescu  <mihail.ionescu@arm.com>

gcc/doc/sourcebuild.texi

@@ -1971,6 +1971,14 @@ ARM Target supports options suitable for accessing the Q-bit manipulation
 intrinsics from @code{arm_acle.h}.
 Some multilibs may be incompatible with these options.
 
+@item arm_softfp_ok
+@anchor{arm_softfp_ok}
+ARM target supports the @code{-mfloat-abi=softfp} option.
+
+@item arm_hard_ok
+@anchor{arm_hard_ok}
+ARM target supports the @code{-mfloat-abi=hard} option.
+
 @end table
 
 @subsubsection AArch64-specific attributes

gcc/testsuite/ChangeLog

+2020-04-22  Christophe Lyon  <christophe.lyon@linaro.org>
+
+        * lib/target-supports.exp (arm_softfp_ok): New effective target.
+        (arm_hard_ok): Likewise.
+
 2020-04-22  Tobias Burnus  <tobias@codesourcery.com>
 
 	PR fortran/94709

gcc/testsuite/lib/target-supports.exp

@@ -4739,6 +4739,26 @@ proc check_effective_target_default_branch_protection { } {
     return [check_configured_with "enable-standard-branch-protection"]
 }
 
+# Return 1 if this is an ARM target supporting -mfloat-abi=softfp.
+
+proc check_effective_target_arm_softfp_ok { } {
+    return [check_no_compiler_messages arm_softfp_ok object {
+	#include <stdint.h>
+	int dummy;
+	int main (void) { return 0; }
+	} "-mfloat-abi=softfp"]
+}
+
+# Return 1 if this is an ARM target supporting -mfloat-abi=hard.
+
+proc check_effective_target_arm_hard_ok { } {
+    return [check_no_compiler_messages arm_hard_ok object {
+	#include <stdint.h>
+	int dummy;
+	int main (void) { return 0; }
+	} "-mfloat-abi=hard"]
+}
+
 # Return 1 if the target supports ARMv8.1-M MVE with floating point
 # instructions, 0 otherwise.  The test is valid for ARM.
 # Record the command line options needed.