Add patch to fix compilation of boost with compilers not in path (#29718)

Co-authored-by: Mikael Simberg <mikael.simberg@iki.if>

var/spack/repos/builtin/packages/boost/bootstrap-compiler.patch

@@ -0,0 +1,13 @@
+diff --git a/bootstrap.sh b/bootstrap.sh
+index 654801e21f..3331483aa5 100755
+--- a/bootstrap.sh
++++ b/bootstrap.sh
+@@ -226,7 +226,7 @@ rm -f config.log
+ if test "x$BJAM" = x; then
+   $ECHO "Building B2 engine.."
+   pwd=`pwd`
+-  CXX= CXXFLAGS= "$my_dir/tools/build/src/engine/build.sh" ${TOOLSET}
++  CXXFLAGS= "$my_dir/tools/build/src/engine/build.sh" ${TOOLSET} --cxx="$CXX"
+   if [ $? -ne 0 ]; then
+       echo
+       echo "Failed to build B2 build engine"

var/spack/repos/builtin/packages/boost/package.py

@@ -301,6 +301,9 @@ def libs(self):
     # and https://github.com/spack/spack/pull/21408
     patch("bootstrap-toolset.patch", when="@1.75")
 
+    # Fix compiler used for building bjam during bootstrap
+    patch("bootstrap-compiler.patch", when="@1.76:")
+
     # Allow building context asm sources with GCC on Darwin
     # See https://github.com/spack/spack/pull/24889
     # and https://github.com/boostorg/context/issues/177