improve abort identification in KLEE output

KLEE reports the line that called `ll::abort()`. The previous
solution called a safe `abort()` which in turn called `ll::abort`. This
meant that every abort was reported as originating in this library.

This replaces the safe `abort()` function with a macro `kabort!()`. The
behavior differs in that `kabort!()` expands to nothing when not in KLEE
mode, while `abort()` expanded to a panic.

The macro causes the call to `ll::abort()` to happen directly from user
code from KLEE's point of view.

klee-examples/examples/modify.rs

@@ -22,6 +22,6 @@ fn main() {
     }
 
     if rw.read() == 0 {
-        klee::abort(); // we directly call the intrinsic abort
+        klee::kabort!(); // we directly call the intrinsic abort
     }
 }

klee-examples/src/peripheral.rs

@@ -18,7 +18,7 @@ fn main() {
     }
     if dwt.ctrl.read() == 0 {
         if dwt.ctrl.read() == 0 {
-            klee::abort();
+            klee::kabort!();
         };
     };
 }

klee-examples/src/register.rs

@@ -51,7 +51,7 @@ fn main() {
 
     if rw.read() == 0 {
         if rw.read() == 0 {
-            klee::abort();
+            klee::kabort!();
         }
     }
 }

src/lib.rs

@@ -16,15 +16,13 @@ use core::ffi::c_void;
 #[doc(hidden)]
 pub use cstr_core::CStr;
 
+/// Aborts the path in KLEE mode, does nothing otherwise
+#[macro_export]
+macro_rules! kabort {
+    () => {
         #[cfg(feature = "klee-analysis")]
-#[inline(always)]
-pub fn abort() -> ! {
-    unsafe { ll::abort() }
-}
-
-#[cfg(not(feature = "klee-analysis"))]
-pub fn abort() -> ! {
-    panic!(); // leads to the defined panic handler
+        unsafe { $crate::ll::abort() };
+    };
 }
 
 #[cfg(feature = "klee-analysis")]
@@ -60,18 +58,16 @@ macro_rules! ksymbol {
     };
 }
 
-#[cfg(feature = "klee-analysis")]
+/// If in KLEE mode, the assertion is made.
+/// Otherwise, this is does nothing.
 #[macro_export]
 macro_rules! kassert {
     ($e:expr) => {
+        #[cfg(feature = "klee-analysis")]
+        {
             if !$e {
-            $crate::abort();
+                $crate::kabort!();
             }
-    };
         }
-
-#[cfg(not(feature = "klee-analysis"))]
-#[macro_export]
-macro_rules! kassert {
-    ($e:expr) => {};
+    };
 }