configure: Remove the check for the __thread keyword

We recently bumped our minimum required version of GCC to 7.4
and Clang to 6.0, and those compiler versions should support
the __thread keyword already.

Signed-off-by: Thomas Huth <thuth@redhat.com>
Message-Id: <20211028185910.1729744-2-thuth@redhat.com>
Reviewed-by: Richard Henderson <richard.henderson@linaro.org>
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>

configure

@@ -1724,17 +1724,6 @@ if test "$static" = "yes" ; then
   fi
 fi
 
-# Unconditional check for compiler __thread support
-  cat > $TMPC << EOF
-static __thread int tls_var;
-int main(void) { return tls_var; }
-EOF
-
-if ! compile_prog "-Werror" "" ; then
-    error_exit "Your compiler does not support the __thread specifier for " \
-	"Thread-Local Storage (TLS). Please upgrade to a version that does."
-fi
-
 cat > $TMPC << EOF
 
 #ifdef __linux__