[gcc r14-9143] doc: RISC-V: Document that -mcpu doesn't override -march or -mtune

[gcc r14-9143] doc: RISC-V: Document that -mcpu doesn't override -march or -mtune

[Kito Cheng]

https://gcc.gnu.org/g:1c5da882bf77400748aeb0b01bf9a7faba1a4f32

commit r14-9143-g1c5da882bf77400748aeb0b01bf9a7faba1a4f32
Author: Palmer Dabbelt <palmer@rivosinc.com>
Date:   Tue Feb 20 07:45:38 2024 -0800

    doc: RISC-V: Document that -mcpu doesn't override -march or -mtune
    
    This came up recently as Edwin was looking through the test suite.  A
    few of us were talking about this during the patchwork meeting and were
    surprised.  Looks like this is the desired behavior, so let's at least
    document it.
    
    gcc/ChangeLog:
    
            * doc/invoke.texi: Document -mcpu.
    
    Signed-off-by: Palmer Dabbelt <palmer@rivosinc.com>

Diff:
---
 gcc/doc/invoke.texi | 2 ++
 1 file changed, 2 insertions(+)

diff --git a/gcc/doc/invoke.texi b/gcc/doc/invoke.texi
index 58527e1ea3c5..4f4ca2b76720 100644
--- a/gcc/doc/invoke.texi
+++ b/gcc/doc/invoke.texi
@@ -30750,6 +30750,8 @@ Permissible values for this option are: @samp{sifive-e20}, @samp{sifive-e21},
 @samp{sifive-u54}, @samp{sifive-u74}, @samp{sifive-x280}, @samp{sifive-xp450},
 @samp{sifive-x670}.
 
+Note that @option{-mcpu} does not override @option{-march} or @option{-mtune}.
+
 @opindex mtune
 @item -mtune=@var{processor-string}
 Optimize the output for the given processor, specified by microarchitecture or