Mitigate issues related to compiler options when cross-compiling (#21330)

* Document C compiler options config when cross-compiling

* Allow empty string to override default

1 files changed, 5 insertions, 3 deletions

diff --git a/doc/nimc.md b/doc/nimc.md
index 81a060d8a..7b0e99e06 100644
--- a/doc/nimc.md
+++ b/doc/nimc.md
@@ -316,14 +316,16 @@ Another way is to make Nim invoke a cross compiler toolchain:
   nim c --cpu:arm --os:linux myproject.nim
   ```
 
-For cross compilation, the compiler invokes a C compiler named
-like `$cpu.$os.$cc` (for example arm.linux.gcc) and the configuration
-system is used to provide meaningful defaults. For example for `ARM` your
+For cross compilation, the compiler invokes a C compiler named like
+`$cpu.$os.$cc` (for example `arm.linux.gcc`) with options defined in
+`$cpu.$os.$cc.options.always`. The configuration system is used to provide
+meaningful defaults. For example, for Linux on a 32-bit ARM CPU, your
 configuration file should contain something like:
 
     arm.linux.gcc.path = "/usr/bin"
     arm.linux.gcc.exe = "arm-linux-gcc"
     arm.linux.gcc.linkerexe = "arm-linux-gcc"
+    arm.linux.gcc.options.always = "-w -fmax-errors=3"
 
 Cross-compilation for Windows
 =============================