Update 1986/marshall about gcc versus clang

The file compilers.md has been added with rewording of the README.md
(which has naturally been updated as well) and there is some fun in it
too.

1986/marshall/README.md

@@ -8,13 +8,13 @@ Eric Marshall
 make all
 ```
 
-There is an alternate version. See the [Alternate code](#alternate-code) section
-for the commentary on why this is: there was a funny problem in modern systems
-where depending on the compiler and the optimiser it would work with one
-compiler with the optimiser but it would not work with the other; and if the
-optimiser state is changed the previous problematic compiler might work but the
-other one would not. We describe this in more detail below and we encourage you
-to read it for entertainment if nothing else.
+There is an [alternate version](#alternate-code). The reason is a funny problem:
+in modern systems, depending on the platform, compiler and the optimiser, it
+would work with one compiler with the optimiser but it would not work with the
+other; and if the optimiser state is changed the previous problematic compiler
+might work but the other one would not. We describe this in more detail in
+[compilers.md](compilers.md) and we encourage you to read it for entertainment
+if nothing else.
 
 
 ## Try:
@@ -25,93 +25,29 @@ to read it for entertainment if nothing else.
 
 ## Alternate code:
 
-As some changes had to be made due to the problem of conflicting compiler
-options briefly noted above we provide the code that demonstrates the problem so
-you can see if your compiler has the problem as described below.
+Due to the different [conflicting problems](compilers.md) with gcc and clang, we
+instead offer the problematic code as an alternate version whereas
+[marshall.c](marshall.c) has both the infinite loop and the complicated arg to
+`_exit()` commented out, changing the value passed into `_exit()` to `1`.
 
-In some versions of gcc and clang (this was first discovered in fedora linux 38)
-if the compiler was enabled one compiler would generate code that segfaulted but
-the other one would not. However, when then disabling the optimiser the compiler
-that had no problem suddenly did and the one that did suddenly did not.
+### Alternate build:
 
-Another problem was that depending on the optimiser an infinite loop would be
-entered.
+To see if your compiler has the problems noted:
 
-The alternate code has the original fix for clang which works with some
-compilers depending on the optimiser. When we refer to the code below we refer
-to the alternate code.
-
-#### The conflicting compiler problems:
-
-Below we describe the conflicting options that resulted in the need to modify
-the original code.
-
-##### Linux
-
-With the optimiser disabled GCC compiled the code to enter an infinite loop.
-Enabling the optimiser and it worked fine. But if the optimiser is enabled clang
-generates code that first prints the text twice (it should print it once) and
-then immediately dumps core!
-
-But then there's that infinite loop. What happens if we remove it?
-
-Once the loop is removed if we compile with clang and the optimiser is disabled
-all is okay. If however we compile with gcc and the optimiser is disabled the
-string is printed once and then the program dumps core! Why is this? It is
-because of the call to `_exit()` (see below). Clang works fine with the loop
-removed and the optimiser disabled. If however we enable the optimiser clang
-will generate code that prints the string twice and dumps core just like before!
-What about the call to `_exit()`?
-
-The call was:
-
-
-```c
-_exit(argv[(int)*argc-2/cc[1*(int)*argc]|-1<<4]);
-```
-
-Changing it to not refer to these variables and just exit 1 and the problems
-disappear!
-
-##### macOS
-
-But as noted just because it works one way in linux does not mean it works the
-same way in macOS.
-
-If the infinite loop is not removed/commented out and the optimiser is enabled
-it works fine but if it's disabled it prints out the string and then enters an
-infinite loop.
-
-After we fix the infinite loop if we change the `_exit()` call in macOS and
-disable the optimiser we might get something like:
-
-```sh
-$ ./marshall
-      choo choo
-Segmentation fault: 11
-```
-
-Observe how it doesn't print it twice. But of course it segfaults so it's not
-right either.
-
-If the optimiser is enabled, however, we will see that it works fine before the
-change to `_exit()`.
-
-
-### Alternate use:
-
-Due to the different conflicting problems with gcc and clang, we instead offer
-the problematic code as an alternate version whereas [marshall.c](marshall.c)
-has both the infinite loop and the complicated arg to `_exit()` commented out,
-changing the value passed into `_exit()` to `1`.
-
-To try out the alternate version:
 
 ```sh
 make alt
 ```
 
-Use `marshall.alt` as you would `marshall` above.
+### Alternate run:
+
+```sh
+./marshall.alt
+```
+
+Does it work in your system? That is does it not segfault, does it print it only
+once and does it not enter an infinite loop? Or more generally does it print the
+text exactly once and then exit?
 
 
 ## Judges' remarks: