Use "-pipe" option for gcc-15 and latest clang

Author: igaztanaga

.github/workflows/ci.yml

@@ -135,6 +135,7 @@ jobs:
           # Linux, gcc-15
           - toolset: gcc-15
             cxxstd: "11,14,17,20,23,2c"
+            cxxflags: -pipe
             os: ubuntu-latest
             container: ubuntu:26.04
             install: g++-15-multilib
@@ -325,13 +326,15 @@ jobs:
           - toolset: clang
             compiler: clang++-19
             cxxstd: "03,11,14,17,20,2b"
+            cxxflags: -pipe
             container: ubuntu:24.04
             os: ubuntu-latest
             install: clang-19
           # Linux, clang-20
           - toolset: clang
             compiler: clang++-20
             cxxstd: "11,14,17,20,23,2c"
+            cxxflags: -pipe
             container: ubuntu:26.04
             os: ubuntu-latest
             install: clang-20