compiler.get_supported_arguments reports success for unsupported flags

The has_argument and get_supported_argument methods are reporting success when the compiler returns an unsupported flag error to stderr.

I have attached a simple test case which demonstrates the error. The relevant meson.log entry is

Running compile:
Working directory:  /tmp/tmpygkykj04
Command line:  c++ /tmp/tmpygkykj04/testfile.cpp -pipe -D_FILE_OFFSET_BITS=64 -c -o /tmp/tmpygkykj04/output.obj -O0 -fpermissive -Wdeclaration-after-statement 

Code:
 int i;

Compiler stdout:
 
Compiler stderr:
 cc1plus: warning: command line option '-Wdeclaration-after-statement' is valid for C/ObjC but not for C++

Compiler for C++ supports arguments -Wdeclaration-after-statement: YES

meson.build.txt