Partial LTO (#1789)

* initial partial LTO example

* Add select private key related files to ignore LTO

* Apply to keystores

beacon_chain/keystore_management.nim

@@ -11,6 +11,7 @@ export
   keystore
 
 {.push raises: [Defect].}
+{.localPassC: "-fno-lto".} # no LTO for crypto
 
 const
   keystoreFileName* = "keystore.json"

beacon_chain/spec/keystore.nim

@@ -23,6 +23,7 @@ export
   results, burnMem, writeValue, readValue
 
 {.push raises: [Defect].}
+{.localPassC: "-fno-lto".} # no LTO for crypto
 
 type
   ChecksumFunctionKind* = enum

nim.cfg

@@ -0,0 +1,35 @@
+# ############################################################
+#
+#                    No LTO for crypto
+#
+# ############################################################
+
+# This applies per-file compiler flags to C files
+# which do not support {.localPassC: "-fno-lto".}
+# Unfortunately this is filename based instead of path-based
+# Assumes GCC
+
+# BLST
+server.always = "-fno-lto"
+assembly.always = "-fno-lto"
+
+# Secp256k1
+secp256k1.always = "-fno-lto"
+
+# BearSSL - only RNGs
+aesctr_drbg.always = "-fno-lto"
+hmac_drbg.always = "-fno-lto"
+sysrng.always = "-fno-lto"
+
+# Miracl - only ECP to derive public key from private key
+ecp_BLS12381.always = "-fno-lto"
+
+# ############################################################
+#
+#                    Spurious warnings
+#
+# ############################################################
+
+# sqlite3.c: In function ‘sqlite3SelectNew’:
+# vendor/nim-sqlite3-abi/sqlite3.c:124500: warning: function may return address of local variable [-Wreturn-local-addr]
+sqlite3.always = "-fno-lto" # -Wno-return-local-addr