Partial revert of #105301 to fix build break (#105785)

Author: jkotas

eng/common/native/init-compiler.sh

@@ -19,19 +19,19 @@ case "$compiler" in
         # clangx.y or clang-x.y
         version="$(echo "$compiler" | tr -d '[:alpha:]-=')"
         majorVersion="${version%%.*}"
+        [ -z "${version##*.*}" ] && minorVersion="${version#*.}"
 
-        # LLVM based on v18 released in early 2024, with two releases per year
-        maxVersion="$((18 + ((($(date +%Y) - 2024) * 12 + $(date +%m) - 3) / 6)))"
+        if [ -z "$minorVersion" ] && [ -n "$majorVersion" ] && [ "$majorVersion" -le 6 ]; then
+            minorVersion=0;
+        fi
         compiler=clang
         ;;
 
     gcc*|-gcc*|--gcc*)
         # gccx.y or gcc-x.y
         version="$(echo "$compiler" | tr -d '[:alpha:]-=')"
         majorVersion="${version%%.*}"
-
-        # GCC based on v14 released in early 2024, with one release per year
-        maxVersion="$((14 + ((($(date +%Y) - 2024) * 12 + $(date +%m) - 3) / 12)))"
+        [ -z "${version##*.*}" ] && minorVersion="${version#*.}"
         compiler=gcc
         ;;
 esac
@@ -49,10 +49,12 @@ check_version_exists() {
     desired_version=-1
 
     # Set up the environment to be used for building with the desired compiler.
-    if command -v "$compiler-$1" > /dev/null; then
-        desired_version="-$1"
-    elif command -v "$compiler$1" > /dev/null; then
-        desired_version="$1"
+    if command -v "$compiler-$1.$2" > /dev/null; then
+        desired_version="-$1.$2"
+    elif command -v "$compiler$1$2" > /dev/null; then
+        desired_version="$1$2"
+    elif command -v "$compiler-$1$2" > /dev/null; then
+        desired_version="-$1$2"
     fi
 
     echo "$desired_version"
@@ -73,7 +75,7 @@ set_compiler_version_from_CC() {
     fi
 
     # gcc and clang often display 3 part versions. However, gcc can show only 1 part in some environments.
-    IFS=. read -r majorVersion _ <<EOF
+    IFS=. read -r majorVersion minorVersion _ <<EOF
 $version
 EOF
 }
@@ -82,29 +84,43 @@ if [ -z "$CLR_CC" ]; then
 
     # Set default versions
     if [ -z "$majorVersion" ]; then
-        minVersion=8
-        maxVersion="$((maxVersion + 1))" # +1 for headspace
-        i="$maxVersion"
-        while [ "$i" -ge $minVersion ]; do
-            desired_version="$(check_version_exists "$i")"
-            if [ "$desired_version" != "-1" ]; then majorVersion="$i"; break; fi
-            i=$((i - 1))
+        # note: gcc (all versions) and clang versions higher than 6 do not have minor version in file name, if it is zero.
+        if [ "$compiler" = "clang" ]; then versions="18 17 16 15 14 13 12 11 10 9 8 7 6.0 5.0 4.0 3.9 3.8 3.7 3.6 3.5"
+        elif [ "$compiler" = "gcc" ]; then versions="14 13 12 11 10 9 8 7 6 5 4.9"; fi
+
+        for version in $versions; do
+            _major="${version%%.*}"
+            [ -z "${version##*.*}" ] && _minor="${version#*.}"
+            desired_version="$(check_version_exists "$_major" "$_minor")"
+            if [ "$desired_version" != "-1" ]; then majorVersion="$_major"; break; fi
         done
 
         if [ -z "$majorVersion" ]; then
             if ! command -v "$compiler" > /dev/null; then
-                echo "Error: No compatible version of $compiler was found within the range of $minVersion to $maxVersion. Please upgrade your toolchain or specify the compiler explicitly using CLR_CC and CLR_CXX environment variables."
+                echo "Error: No usable version of $compiler found."
                 exit 1
             fi
 
             CC="$(command -v "$compiler" 2> /dev/null)"
             CXX="$(command -v "$cxxCompiler" 2> /dev/null)"
             set_compiler_version_from_CC
+        else
+            if [ "$compiler" = "clang" ] && [ "$majorVersion" -lt 5 ] && { [ "$build_arch" = "arm" ] || [ "$build_arch" = "armel" ]; }; then
+                # If a major version was provided explicitly, and it was too old, find a newer compiler instead
+                if ! command -v "$compiler" > /dev/null; then
+                    echo "Error: Found clang version $majorVersion which is not supported on arm/armel architectures, and there is no clang in PATH."
+                    exit 1
+                fi
+
+                CC="$(command -v "$compiler" 2> /dev/null)"
+                CXX="$(command -v "$cxxCompiler" 2> /dev/null)"
+                set_compiler_version_from_CC
+            fi
         fi
     else
-        desired_version="$(check_version_exists "$majorVersion")"
+        desired_version="$(check_version_exists "$majorVersion" "$minorVersion")"
         if [ "$desired_version" = "-1" ]; then
-            echo "Error: Could not find specific version of $compiler: $majorVersion."
+            echo "Error: Could not find specific version of $compiler: $majorVersion $minorVersion."
             exit 1
         fi
     fi