v.help: update v help build, mention -prod -cflags -fno-inline-small-functions as workaround for issues with modern gcc

Author: spytheman

vlib/v/help/build/build.txt

@@ -102,6 +102,8 @@ NB: the build flags are shared with the run command too:
     Compile the executable in production mode, where most optimizations are enabled.
     Note that most V warnings turn to errors, if you pass -prod, so you will have
     to fix them first.
+    Note: gcc versions > 12.0 often have issues with inlining, that manifest with `-prod`.
+    To work around them, you can use `-prod -cflags -fno-inline-small-functions` .
 
   -no-prod-options
     Useful in combination with -prod and -cflags, for allowing more complete customisation,
@@ -110,7 +112,9 @@ NB: the build flags are shared with the run command too:
     will compile the program, without passing `-O3` and `-flto`, that would otherwise
     have been used, but passing `-Os` instead. Note, since `-prod` is used, the V compiler
     itself will still compile your potential `$if prod {` branches, and it will still do the
-    optimisations on the V side, that -prod enables.
+    optimisations on the V side, that -prod enables. You can also use it to compile programs
+    with different optimisation options passed to the C compiler, like `-O2` instead of
+    the default ones, which can be beneficial for working with older or newer buggy compilers.
 
   -no-bounds-checking
     Programs compiled with this option, will do no runtime checking of array access operations.